Nucleophile specificity in chymotrypsin peptide synthesis.

The partitioning of the acylenzyme acetyl-(Gly)n-Phe(NO2)-chymotrypsin (n = 0,1,2) to peptide and peptide acid is observed spectrophotometrically. Values of partitioning ratios for various nucleophiles are calculated from the spectral data. They are a measure for the "true" nucleophile reactivity and are useful in the prediction of the best experimental conditions in enzymic peptide synthesis. A large difference in the nucleophile reactivity is observed which is attributed to the S'2-P'2 interaction.