L-Threonine

Biological Agents -> Amino Acids and Derivatives

Biological Agents -> Amino Acids and Derivatives

Cosmetic ingredients (Threonine) -> CIR (Cosmetic Ingredient Review)

Hair conditioning; Antistatic

log Kow = -2.94

-2.94

Colorless crystals

Crystals

Insoluble in ethanol, ethyl ether, chloroform

Insoluble in common neutral solvents

In water, 9.70X10+4 mg/L at 25 °C

97.0 mg/mL

Sparingly soluble in water; Soluble in buffer systems pH 5.5

256 °C (decomposes)

MP: 228-229 °C with decomposition (dl-threonine); 255-275 °C with decomposition (l(-)-threonine) (naturally occurring); 250-252 °C (dl-allo-threonine)

256 °C

Solid; [Merck Index]

Hemihydrate: Solid; [Merck Index] White powder; [Sigma-Aldrich MSDS]

Solid

White crystalline powder; slight savoury aroma

Positive

2.35

2.7

Agilent XCT

Electrospray ionization

formic acid (5.3nM)

This chemical does not meet GHS hazard criteria for 99.6% (245 of 246) of all reports.

Not Classified

Aggregated GHS information provided per 246 reports by companies from 3 notifications to the ECHA C&L Inventory.

This chemical does not meet GHS hazard criteria for 92.2% (214 of 232) of all reports.

Not Classified

Aggregated GHS information provided per 232 reports by companies from 2 notifications to the ECHA C&L Inventory.

Chemical: L-Threonine

Chemical: DL-Threonine

Regulation (EC) No 1831/2003 (amended)

Status: Active Update: 07-04-2022 https://echa.europa.eu/registration-dossier/-/registered-dossier/16986

L-Threonine: Does not have an individual approval but may be used under an appropriate group standard

Threonine, (2R,3S)-rel-: Does not have an individual approval but may be used under an appropriate group standard

IMAP assessments - DL-Threonine: Environment tier I assessment

IMAP assessments - L-Threonine: Environment tier I assessment

May cause irritation; [Sigma-Aldrich MSDS]

May cause irritation; [Sigma-Aldrich MSDS]

L-Threonine is a food additive permitted for direct addition to food for human consumption, as long as 1) the quantity of the substance added to food does not exceed the amount reasonably required to accomplish its intended physical, nutritive, or other technical effect in food, and 2) any substance intended for use in or on food is of appropriate food grade and is prepared and handled as a food ingredient.

Drug products containing certain active ingredients offered over-the-counter (OTC) for certain uses. A number of active ingredients have been present in OTC drug products for various uses, as described below. However, based on evidence currently available, there are inadequate data to establish general recognition of the safety and effectiveness of these ingredients for the specified uses: threonine is included in weight control drug products.

Threonine used as a nutrient and/or dietary supplement in animal drugs, feeds, and related products is generally recognized as safe when used in accordance with good manufacturing or feeding practice.

NAS, Food and Nutrition Board, Institute of Medicine; Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). National Academy Press, Washington, D.C. (2009).[Available from, as of March 10, 2010: http://www.nap.edu/catalog/10490.html]

Not Classified

Not Classified

SRP: Expired or waste pharmaceuticals shall carefully take into consideration applicable DEA, EPA, and FDA regulations. It is not appropriate to dispose by flushing the pharmaceutical down the toilet or discarding to trash. If possible return the pharmaceutical to the manufacturer for proper disposal being careful to properly label and securely package the material. Alternatively, the waste pharmaceutical shall be labeled, securely packaged and transported by a state licensed medical waste contractor to dispose by burial in a licensed hazardous or toxic waste landfill or incinerator.

SRP: At the time of review, regulatory criteria for small quantity disposal are subject to significant revision, however, household quantities of waste pharmaceuticals may be managed as follows: Mix with wet cat litter or coffee grounds, double bag in plastic, discard in trash.

SRP: Criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.

A methionine-threonine-supplemented low (8.5%) casein diet (8.5CMT) reduced symptoms such as proteinuria in nephritic rats without severe protein malnutrition. ... This study ... examined whether or not L-arginine supplementation to 8.5CMT would exacerbate proteinuria and other symptoms in nephritic rats. Male Wistar rats with glomerulonephritis induced by a single intravenous injection of nephrotoxic serum were fed either a 20% casein diet (control), 8.5% casein diet, 8.5CMT, or L-arginine-supplemented 8.5CMT (8.5CMTA) for 16 days. The 8.5CMTA, as compared with the 8.5CMT, aggravated proteinuria and glomerulonephritis. Administration of L-N(G)-nitroarginine methyl ester, an inhibitor of nitric oxide synthase, to 8.5CMTA-fed nephritic rats by drinking water for 14 days canceled the adverse effect of L-arginine on proteinuria and histopathological damage in glomeruli. These results suggest that the supplementation of L-arginine makes exacerbation via nitric oxide production in glomerulonephritis.

Rats fed a low-protein diet and administered 2-(2-nitro-4-trifluoromethylbenzoyl)cyclohexane-1,3-dione (NTBC) orally at 30 umol/kg/day (10 mg/kg/day) or fed a low-protein diet containing 5 ppm NTBC develop lesions to the cornea of the eye within 3-8 days of exposure with an incidence of about 80%. This treatment also produces a marked inhibition of both hepatic and renal 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, an induction of hepatic but not renal tyrosine amino transferase activity, and a marked tyrosinemia in the plasma and aqueous humor. The extent of tyrosinemia and changes in the activity of tyrosine catabolic enzymes are similar to those reported for rats fed a normal protein diet and administered NTBC orally at 30 mumol/kg/day. However, the onset of corneal lesions occurs much earlier in rats fed a low-protein diet. The adverse ocular effects of NTBC can be alleviated by supplementing the low-protein diet with 1% w/w threonine. The protection afforded by threonine inclusion in the diet was not due to any amelioration in the extent of inhibition of hepatic HPPD activity or reduction in the extent of the tyrosinemia as measured 8 days after treatment. Rats fed L-tyrosine at 5% w/w in a low-protein diet rapidly develop lesions to the cornea of the eye, which are associated with a marked tyrosinemia, increased hepatic tyrosine aminotransferase activity, and about a 50% reduction in the activity of hepatic HPPD. The onset of corneal lesions produced by feeding a high tyrosine diet could be delayed, but not prevented, by inclusion of 1% w/w threonine in the low-protein diet. The basis for the beneficial effect of dietary supplementation of threonine in alleviating the corneal lesions produced by NTBC is unclear. However, our findings do illustrate that protein deficiency limits the ability of the rat to respond to a tyrosine load produced by inhibition of HPPD.

The threonine content of most of the infant formulas currently on the market is approximately 20% higher than the threonine concentration in human milk. Due to this high threonine content the plasma threonine concentrations are up to twice as high in premature infants fed these formulas than in infants fed human milk. To study the effect of different threonine intakes on plasma and tissue amino acid concentrations, 24 young male Wistar rats were fed three experimental diets based on a mixture of bovine proteins with a whey protein/casein ratio of 60/40 with different threonine contents [group A, 0.86 g of threonine/100 g (n = 8); group B, 1.03 g of threonine/100 g (n = 8); group C, 2.21 g of threonine/100 g (n = 8)]. Eight animals were fed a typical rat diet based on bovine casein as controls. After a feeding period of 15 d, amino acids were measured in plasma and in homogenates of the cerebral cortex, brain stem, liver, and muscle. There was a significant correlation between threonine intake and plasma threonine levels (r = 0.687, p < 0.001). The plasma threonine concentration correlated significantly with the threonine concentration in the cortex (r = 0.821, p < 0.01) and the brain stem (r = 0.882, p < 0.01). There was a positive significant correlation between threonine and glycine concentrations in the cortex (r = 0.673, p < 0.01), and the brain stem (r = 0.575, p < 0.01), whereas the glycine concentration decreased with increasing threonine intakes in the liver and muscle. The presented data indicate that increasing the threonine in plasma leads to increasing brain glycine and thereby affects the neurotransmitter balance in the brain. This may have consequences for brain development during early postnatal life. Therefore, excessive threonine intake during infant feeding should be avoided.

Safe in the present practices of use and concentration. Ingredient, concentration, and use information are available in documents discoverable at https://cir-reports.cir-safety.org

L-Threonine is a precursor to the amino acids glycine and serine. It acts as a lipotropic in controlling fat build-up in the liver. May help combat mental illness and may be very useful in indigestion and intestinal malfunctions. Also, threonine prevents excessive liver fat. Nutrients are more readily absorbed when threonine is present.

/OTHER TOXICITY INFORMATION/ Threonine also has been studied in low birth weight infants. In a study of 163 low birth weight infants, threonine serum concentrations were directly related to the threonine concentrations of the formula. The authors suggested that threonine intakes should not exceed about 140 mg/kg body weight/day for premature infants.

/OTHER TOXICITY INFORMATION/ There is no evidence that amino acids derived from usual or even high intakes of protein from foodstuffs present any risk.

/OTHER TOXICITY INFORMATION/ Serum threonine concentration was determined during the first month of life in 163 low birthweight infants fed on either human milk, various adapted formulae, or total parenteral nutrition. On the pooled data, a significant positive relationship was found between the serum threonine concentration and threonine intake. However, the increase of the serum threonine level is more marked in the infants with the lowest actual gestational age; with a high threonine intake, the most premature infants have serum threonine levels twice as high (58.1 vs 31.7 uM/dL) as term infants. Therefore, threonine metabolism seems to be impeded in preterm infants. Considering the cord blood concentration of threonine (26.8 +/- 5.1 uM/dL) and the possible hazardous effect of hyperthreoninemia, it is suggested that threonine intake should not exceed 1200 uM (143 mg)/kg bodyweight/day in premature infants and that the amino acid composition of the diet should probably be modified in order to satisfy their protein requirement.

/OTHER TOXICITY INFORMATION/ The threonine content of most of the infant formulas currently on the market is approximately 20% higher than the threonine concentration in human milk. Due to this high threonine content the plasma threonine concentrations are up to twice as high in premature infants fed these formulas than in infants fed human milk. Increasing the threonine in plasma leads to increasing brain glycine and thereby affects the neurotransmitter balance in the brain. This may have consequences for brain development during early postnatal life. Therefore, excessive threonine intake during infant feeding should be avoided.

/LABORATORY ANIMALS: Acute Exposure/ The purpose of this study was to determine whether an addition of dietary limiting amino acids affected urea synthesis in rats fed a low gluten diet. Experiments were done on three groups of rats given diets containing 10% gluten, 10% gluten +0.5% L-lysine or 10% gluten+0.5% L-lysine, 0.2% L-threonine and 0.2% L-methionine for 10 d. The urinary excretion of urea, and the liver concentrations of serine and ornithine decreased with the addition of dietary L-lysine, L-threonine and L-methionine. The fractional and absolute rates of protein synthesis in tissues increased with the treatment of limiting amino acids. The activities of hepatic urea-cycle enzymes was not related to the urea excretion. These results suggest that the addition of limiting amino acids for the low gluten diet controls the protein synthesis in tissues and hepatic ornithine and decline in urea synthesis.

/LABORATORY ANIMALS: Acute Exposure/ Rats quickly recognize and reject diets deficient in an essential amino acid. The purpose of this study was to determine whether the anterior piriform cortex (APC), the site traditionally recognized as the amino acid chemosensor, plays a role in this early behavior. Rats had cannulae implanted bilaterally into the APC, and were injected with either saline vehicle or 2 nmoles of threonine (n = 6 per group). All rats were then fed a diet imbalanced with respect to threonine. The threonine-injected group had first meals of longer duration and consumed more food. These data conformed to expectations derived from earlier studies of responses to the first meal of an amino acid imbalanced diet. /It was concluded/ that the concentration of the dietary limiting amino acid in the APC regulates acceptance and rejection of amino acid deficient diets.

/LABORATORY ANIMALS: Subchronic or Prechronic Exposure/ In weanling pigs, adding 0.5, 1, 2, or 4% L-threonine to a 20% crude protein diet did not change weight gain, food intake, and gain:feed ratios in comparison to the controls.

/LABORATORY ANIMALS: Developmental or Reproductive Toxicity/ The results of neurochemical and behavioral studies in the developing rat suggest that despite numerous possible effects of threonine on brain constituents, moderate hyperthreoninemia does not impair markedly the development of the central nervous system.

/OTHER TOXICITY INFORMATION/ In rats fed 5% threonine added to a 10% casein diet, weight gain was reduced compared to controls fed casein alone but there were no changes in liver weight or hepatic DNA, RNA, or protein content.

/SRP:/ Immediate first aid: Ensure that adequate decontamination has been carried out. If patient is not breathing, start artificial respiration, preferably with a demand valve resuscitator, bag-valve-mask device, or pocket mask, as trained. Perform CPR if necessary. Immediately flush contaminated eyes with gently flowing water. Do not induce vomiting. If vomiting occurs, lean patient forward or place on the left side (head-down position, if possible) to maintain an open airway and prevent aspiration. Keep patient quiet and maintain normal body temperature. Obtain medical attention. /Poisons A and B/

/SRP:/ Basic treatment: Establish a patent airway (oropharyngeal or nasopharyngeal airway, if needed). Suction if necessary. Watch for signs of respiratory insufficiency and assist ventilations if needed. Administer oxygen by nonrebreather mask at 10 to 15 L/min. Monitor for pulmonary edema and treat if necessary ... . Monitor for shock and treat if necessary ... . Anticipate seizures and treat if necessary ... . For eye contamination, flush eyes immediately with water. Irrigate each eye continuously with 0.9% saline (NS) during transport ... . Do not use emetics. For ingestion, rinse mouth and administer 5 mL/kg up to 200 mL of water for dilution if the patient can swallow, has a strong gag reflex, and does not drool ... . Cover skin burns with dry sterile dressings after decontamination ... . /Poisons A and B/

/SRP:/ Advanced treatment: Consider orotracheal or nasotracheal intubation for airway control in the patient who is unconscious, has severe pulmonary edema, or is in severe respiratory distress. Positive-pressure ventilation techniques with a bag valve mask device may be beneficial. Consider drug therapy for pulmonary edema ... . Consider administering a beta agonist such as albuterol for severe bronchospasm ... . Monitor cardiac rhythm and treat arrhythmias as necessary ... . Start IV administration of D5W /SRP: "To keep open", minimal flow rate/. Use 0.9% saline (NS) or lactated Ringer's if signs of hypovolemia are present. For hypotension with signs of hypovolemia, administer fluid cautiously. Watch for signs of fluid overload ... . Treat seizures with diazepam or lorazepam ... . Use proparacaine hydrochloride to assist eye irrigation ... . /Poisons A and B/

L-Threonine is a food additive permitted for direct addition to food for human consumption, as long as 1) the quantity of the substance added to food does not exceed the amount reasonably required to accomplish its intended physical, nutritive, or other technical effect in food, and 2) any substance intended for use in or on food is of appropriate food grade and is prepared and handled as a food ingredient.

Drug products containing certain active ingredients offered over-the-counter (OTC) for certain uses. A number of active ingredients have been present in OTC drug products for various uses, as described below. However, based on evidence currently available, there are inadequate data to establish general recognition of the safety and effectiveness of these ingredients for the specified uses: threonine is included in weight control drug products.

Threonine used as a nutrient and/or dietary supplement in animal drugs, feeds, and related products is generally recognized as safe when used in accordance with good manufacturing or feeding practice.

An essential amino acid occurring naturally in the L-form, which is the active form. It is found in eggs, milk, gelatin, and other proteins.

Table: Comparison of the Pool Sizes of Free and Protein-Bound Amino Acids in Rat Muscle [Table#7472]

An experimental formula based on acid whey without GMP and a formula based on sweet whey with rich glycomacropeptide(GMP) (threonine content 17.2% higher than in the experimental formula) but otherwise with identical composition were tested with particular respect to threonine metabolism. Fourteen preterm infants appropriate for gestational age were enrolled in this randomized cross-over study. After a feeding period of at least 7 days, the nutrition of each infant was switched to the other formula for the second feeding period. At the end of each feeding period, the concentrations of creatinine and amino acids in the plasma and in the urine were measured. In the plasma, the threonine concentration was significantly lower in the group fed the experimental GMP-free formula than in the group fed the sweet whey formula (P < 0.001). Renal excretion of all essential amino acids was generally very low and less than 2% of the intake, indicating that the kidneys had no marked homeostatic function with respect to plasma amino acid. The plasma concentrations of the threonine metabolites glycine and serine, and that of urea were not influenced by diet. Feeding a whey protein-predominant bovine milk produced from acid whey protein reduces significantly the hyperthreoninemia commonly found in formula-fed preterm infants. Thus, acid whey formulas should be recommended for feeding preterm infants.

Calculation of Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for Threonine for Children Ages 7 Months Through 18 Years [Table#7473]

For more Bionecessity (Complete) data for L-Threonine (22 total), please visit the HSDB record page.

L-Threonine is an essential amino acid that helps to maintain the proper protein balance in the body. It is important for the formation of collagen, elastin, and tooth enamel, and aids liver and lipotropic function when combined with aspartic acid and methionine.

L-Threonine is a precursor to the amino acids glycine and serine. It acts as a lipotropic in controlling fat build-up in the liver. May help combat mental illness and may be very useful in indigestion and intestinal malfunctions. Also, threonine prevents excessive liver fat. Nutrients are more readily absorbed when threonine is present.

Amino acids are selected for protein synthesis by binding with transfer RNA (tRNA) in the cell cytoplasm. The information on the amino acid sequence of each individual protein is contained in the sequence of nucleotides in the messenger RNA (mRNA) molecules, which are synthesized in the nucleus from regions of DNA by the process of transcription. The mRNA molecules then interact with various tRNA molecules attached to specific amino acids in the cytoplasm to synthesize the specific protein by linking together individual amino acids; this process, known as translation, is regulated by amino acids (e.g., leucine), and hormones. Which specific proteins are expressed in any particular cell and the relative rates at which the different cellular proteins are synthesized, are determined by the relative abundances of the different mRNAs and the availability of specific tRNA-amino acid combinations, and hence by the rate of transcription and the stability of the messages. From a nutritional and metabolic point of view, it is important to recognize that protein synthesis is a continuing process that takes place in most cells of the body. In a steady state, when neither net growth nor protein loss is occurring, protein synthesis is balanced by an equal amount of protein degradation. The major consequence of inadequate protein intakes, or diets low or lacking in specific indispensable amino acids relative to other amino acids (often termed limiting amino acids), is a shift in this balance so that rates of synthesis of some body proteins decrease while protein degradation continues, thus providing an endogenous source of those amino acids most in need. /Protein synthesis/

The mechanism of intracellular protein degradation, by which protein is hydrolyzed to free amino acids, is more complex and is not as well characterized at the mechanistic level as that of synthesis. A wide variety of different enzymes that are capable of splitting peptide bonds are present in cells. However, the bulk of cellular proteolysis seems to be shared between two multienzyme systems: the lysosomal and proteasomal systems. The lysosome is a membrane-enclosed vesicle inside the cell that contains a variety of proteolytic enzymes and operates mostly at acid pH. Volumes of the cytoplasm are engulfed (autophagy) and are then subjected to the action of the protease enzymes at high concentration. This system is thought to be relatively unselective in most cases, although it can also degrade specific intracellular proteins. The system is highly regulated by hormones such as insulin and glucocorticoids, and by amino acids. The second system is the ATP-dependent ubiquitin-proteasome system, which is present in the cytoplasm. The first step is to join molecules of ubiquitin, a basic 76-amino acid peptide, to lysine residues in the target protein. Several enzymes are involved in this process, which selectively targets proteins for degradation by a second component, the proteasome. /Protein degradation/

Hepatic

The evidence indicates that excess threonine is converted to carbohydrate, liver lipids, and carbon dioxide.

L-Threonine is a large neutral amino acid that is indispensable. ... L-threonine does not take part in transamination reactions.

Once the amino acid deamination products enter the tricarboxylic acid (TCA) cycle (also known as the citric acid cycle or Krebs cycle) or the glycolytic pathway, their carbon skeletons are also available for use in biosynthetic pathways, particularly for glucose and fat. Whether glucose or fat is formed from the carbon skeleton of an amino acid depends on its point of entry into these two pathways. If they enter as acetyl-CoA, then only fat or ketone bodies can be formed. The carbon skeletons of other amino acids can, however, enter the pathways in such a way that their carbons can be used for gluconeogenesis. This is the basis for the classical nutritional description of amino acids as either ketogenic or glucogenic (ie, able to give rise to either ketones [or fat] or glucose). Some amino acids produce both products upon degradation and so are considered both ketogenic and glucogenic.

The threonine dehydrogenase (TDG) pathway is a significant route of threonine degradation, yielding glycine in experimental animals, but has not been accurately quantitated in humans. Therefore, the effect of a large excess of dietary threonine, given either as free amino acid (+Thr) or as a constituent of protein (+P-Thr), on threonine catabolism to CO(2) and to glycine was studied in six healthy adult males using a 4-h constant infusion of L-[1-(13)C]threonine and [(15)N]glycine. Gas chromatography-combustion isotope ratio mass spectrometry was used to determine [(13)C]glycine produced from labeled threonine. Threonine intakes were higher on +Thr and +P-Thr diets compared with control (126, 126, and 50 micromol x kg(-1) x h(-1), SD 8, P < 0.0001). Threonine oxidation to CO(2) increased threefold in subjects on +Thr and +P-Thr vs. control (49, 45, and 15 micromol x kg(-1) x h(-1), SD 6, P < 0.0001). Threonine conversion to glycine tended to be higher on +Thr and +P-Thr vs. control (3.5, 3.4, and 1.6 micromol x kg(-1) x h(-1), SD 1.3, P = 0.06). The TDG pathway accounted for only 7-11% of total threonine catabolism and therefore is a minor pathway in the human adult.

For more Metabolism/Metabolites (Complete) data for L-Threonine (8 total), please visit the HSDB record page.

Although the free amino acids dissolved in the body fluids are only a very small proportion of the body's total mass of amino acids, they are very important for the nutritional and metabolic control of the body's proteins. ... Although the plasma compartment is most easily sampled, the concentration of most amino acids is higher in tissue intracellular pools. Typically, large neutral amino acids, such as leucine and phenylalanine, are essentially in equilibrium with the plasma. Others, notably glutamine, glutamic acid, and glycine, are 10- to 50-fold more concentrated in the intracellular pool. Dietary variations or pathological conditions can result in substantial changes in the concentrations of the individual free amino acids in both the plasma and tissue pools. /Amino acids/

After ingestion, proteins are denatured by the acid in the stomach, where they are also cleaved into smaller peptides by the enzyme pepsin, which is activated by the increase in stomach acidity that occurs on feeding. The proteins and peptides then pass into the small intestine, where the peptide bonds are hydrolyzed by a variety of enzymes. These bond-specific enzymes originate in the pancreas and include trypsin, chymotrypsins, elastase, and carboxypeptidases. The resultant mixture of free amino acids and small peptides is then transported into the mucosal cells by a number of carrier systems for specific amino acids and for di- and tri-peptides, each specific for a limited range of peptide substrates. After intracellular hydrolysis of the absorbed peptides, the free amino acids are then secreted into the portal blood by other specific carrier systems in the mucosal cell or are further metabolized within the cell itself. Absorbed amino acids pass into the liver, where a portion of the amino acids are taken up and used; the remainder pass through into the systemic circulation and are utilized by the peripheral tissues. /Amino acids/

About 11 to 15 g of nitrogen are excreted each day in the urine of a healthy adult consuming 70 to 100 g of protein, mostly in the form of urea, with smaller contributions from ammonia, uric acid, creatinine, and some free amino acids. These are the end products of protein metabolism, with urea and ammonia arising from the partial oxidation of amino acids. Uric acid and creatinine are indirectly derived from amino acids as well. The removal of nitrogen from the individual amino acids and its conversion to a form that can be excreted by the kidney can be considered as a two-part process. The first step usually takes place by one of two types of enzymatic reactions: transamination or deamination. Transamination is a reversible reaction that uses ketoacid intermediates of glucose metabolism (e.g., pyruvate, oxaloacetate, and alpha-ketoglutarate) as recipients of the amino nitrogen. Most amino acids can take part in these reactions, with the result that their amino nitrogen is transferred to just three amino acids: alanine from pyruvate, aspartate from oxaloacetate, and glutamate from alpha-ketoglutarate. Unlike many amino acids, branched-chain amino acid transamination occurs throughout the body, particularly in skeletal muscle. Here the main recipients of amino nitrogen are alanine and glutamine (from pyruvate and glutamate, respectively), which then pass into the circulation. These serve as important carriers of nitrogen from the periphery (skeletal muscle) to the intestine and liver. In the small intestine, glutamine is extracted and metabolized to ammonia, alanine, and citrulline, which are then conveyed to the liver via the portal circulation. Nitrogen is also removed from amino acids by deamination reactions, which result in the formation of ammonia. A number of amino acids can be deaminated, either directly (histidine), by dehydration (serine, threonine), by way of the purine nucleotide cycle (aspartate), or by oxidative deamination (glutamate). ... Glutamate is also formed in the specific degradation pathways of arginine and lysine. Thus, nitrogen from any amino acid can be funneled into the two precursors of urea synthesis, ammonia and aspartate.

Although it seems clear that the efficiency of dietary protein digestion (in the sense of removal of amino acids from the small intestinal lumen) is high, there is now good evidence to show that nutritionally significant quantities of indispensable amino acids are metabolized by the tissues of the splanchnic bed, including the mucosal cells of the intestine. Thus, less than 100% of the amino acids removed from the intestinal lumen appear in the peripheral circulation, and the quantities that are metabolized by the splanchnic bed vary among the amino acids, with intestinal threonine metabolism being particularly high.

For more Absorption, Distribution and Excretion (Complete) data for L-Threonine (12 total), please visit the HSDB record page.

CIR ingredient: Threonine

An essential amino acid; [Merck Index] Used as a flavoring agent and nutritional supplement; [FDA] Used as a dietary supplement, flavor additive, and for biochemical research; [HSDB]

An essential amino acid; [Merck Index]

Nutrition and biochemical research, dietary supplement

BIOLOGICAL ACTIVITIES: Possible antiulcer; essential; flavor

Use (kg; approx.) in Germany (2009): >10000

Flavouring Agent -> FLAVOURING_AGENT -> JECFA Functional Classes

Flavoring Agents -> JECFA Flavorings Index

Cosmetics -> Hair conditioning; Antistatic

L-Threonine: ACTIVE

Threonine: ACTIVE

The amino acids that are incorporated into mammalian protein are alpha-amino acids, with the exception of proline, which is an alpha-imino acid. This means that they have a carboxyl group, an amino nitrogen group, and a side chain attached to a central alpha-carbon. Functional differences among the amino acids lie in the structure of their side chains. In addition to differences in size, these side groups carry different charges at physiological pH (e.g., nonpolar, uncharged but polar, negatively charged, positively charged); some groups are hydrophobic (e.g., branched chain and aromatic amino acids) and some hydrophilic (most others). These side chains have an important bearing on the ways in which the higher orders of protein structure are stabilized and are intimate parts of many other aspects of protein function.