ナダイド

解説ニコチンアミドアデニンジヌクレオチド略称NAD．以前は補酵素Ⅰ(CoⅠ)，あるいはDPN(ジホスホピリジンヌクレオチド)ともよばれた．下の表に示したような酸化還元酵素の補酵素で，構造式は次のとおりである．NAD＋は還元型基質から水素を受けとりそれを酸化し，還元型NAD(NADH)と H＋ を生成する．NAD＋の還元は次に示すようにニコチン酸アミドの部位で起こる．この反応は可逆的である．吸湿性の白色の粉末．水に易溶．酵母から単離されるが，ニコチンアミドモノヌクレオチドとアデノシン5′-リン酸との脱水縮合で合成される．NAD＋：[α]D －31.5°(水)．λmax 259 nm(ε 17.6×106)．NADH：[α]D ＋14.8°(水)．λmax 340 nm(ε 6.2×106)．NAD＋が関与するアルコール脱水素酵素の反応は次のように示される． CH3CH2OH ＋ NAD＋⇄ CH3CHO ＋ NADH ＋ H＋ 反応が右へ進行するとき340 nm の吸光度は増加する．これを利用して酵素反応速度を測定することができる．また，NADHはフラビンを介してグルタチオンやシトクロムを還元する作用がある． NADH ＋ H＋ ＋ FAD → NAD＋ ＋ FADH2 FADH2 ＋ 酸化型グルタチオン → FAD ＋ 2還元型グルタチオン また，NAD＋はDNAが切断されたとき，それを修復する酵素DNAリガーゼの作用にも関与する．LD50 4.333 g/kg(マウス，腹腔)．

説明β-Nicotinamide adenine dinucleotide (NAD+) plays a major role in metabolism as a cofactor and mobile electron acceptor. NAD+ is a required oxidizing cosubstrate for many enzymes. It is reduced to NADH (Cat# N-035) which carries electrons to the electron transport chain for subsequent oxidative phorphorylation and ATP production. NAD+ is capable of donating ADP-ribose moieties to a protein, producing nicotinamide in the process. Sirtuin enzymes use NAD+ as a substrate to deacetylate proteins and direct activity between the nucleus and mitochondria. NAD+ is regenerated by fermentation and by oxidative phosphorylation.

来歴β-Nicotinamide adenine dinucleotide was first discovered by British biochemists Arthur Harden and William John Young in 1906. They observed that the addition of boiled and filtered yeast extract significantly increased the rate of alcoholic fermentation in unboiled yeast extracts. They named the unidentified factor responsible for this effect a coferment. By extensively purifying it from yeast extracts, Hans von Euler-Chelpin identified this heat-stable factor as a nucleotide sugar phosphate. In 1936, German scientist Otto Heinrich Warburg demonstrated the role of this nucleotide coenzyme in hydride transfer and determined the nicotinamide portion as the site of redox reactions. Vitamin precursors of NAD+ were first identified in 1938, when Conrad Elvehjem showed that liver has an "anti-black tongue" activity in the form of nicotinamide. Then, in 1939, he provided the first strong evidence that niacin is used to synthesize NAD+.