Pepsin as a catalyst for peptide synthesis: formation of peptide bonds not typical for pepsin substrate specificity

Porcine pepsin in water solutions containing 15–28% of dimethylformamide at pH 5 and 20–
37 C catalysed the formation of peptide bonds between Z-Ala-Ala-Phe-OH and various
amino acid or peptide derivatives. Substrate binding subsite S′ 1 of pepsin demonstrated
broad specificity in these reactions but revealed a certain preference for hydrophobic amino
acid residues, including non-proteinous homophenylalanine, p-nitrophenylalanine, S-
methylcysteine, as well as for those that contained, in addition to the hydrophobic elements,
a group capable of donating a hydrogen bond, eg o-nitrotyrosine. This observation
increases the range of peptides that might be prepared by pepsin-catalysed synthesis