Trifluoroacetic acid → L-Glutamic Acid

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The oligopeptides prepared as described in Example 2 were individually dissolved in PSA digestion buffer (12 mM tris(hydroxymethyl)-aminomethane pH8.0, 25 mM NaCl, 0.5 mM CaCl2) and the solution added to PSA at a molar ration of 100 to 1. Alternatively, the PSA digestion buffer utilized is 50 mM tris(hydroxymethyl)-aminomethane pH7.4, 140 mM NaCl. The reaction is quenched after various reaction times by the addition of trifluoroacetic acid (TFA) to a final 1% (volume/volume). Alternatively the reaction is quenched with 10 nM ZnCl2. The quenched reaction was analyzed by HPLC on a reversed-phase C18 column using an aqueous 0.1% TFA/acetonitrile gradient. The results of the assessment are shown in FIG. 2. Other oligopeptides prepared as described in Example 2 were tested in the same assay wherein the reaction was quenched at 4 hours. Those results of the assessment are shown in FIG. 3. The removal of an asparagine residue from the amino terminus of the oligopeptide results in a significant loss of PSA mediated peptide hydrolysis, while the presence of a glutamic acid residue at the carboxyl end of the peptide appears not to be essential to recognition by PSA.

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