alpha-Chymotrypsin in plastein synthesis: influence of substrate concentration on enzyme activity.

The role of alpha-chymotrypsin in the plastein reaction was studied using a peptic hydrolysate of albumin as substrate. Study of this reaction simultaneously by different methods showed that the plastein reaction is enzyme catalyzed and is highly dependent on environmental conditions. A gel permeation chromatography study of the plastein reaction showed simultaneous increases in the high- and low-molecular-weight oligopeptide fractions; a transpeptidation mechanism may be involved in the reaction. A study of the effect of substrate concentration on the plastein reaction catalyzed by alpha-chymotrypsin showed a profile with both hydrolytic and synthetic activities. This effect was also observed when the reaction course was followed by quantification of the free amino groups at different substrate concentrations, showing that a condensation mechanism is responsible for the synthetic activity when the substrate concentration is very high. These results have led us to conclude that the plastein reaction involves a transpeptidation and/or condensation mechanism, which is a function of the substrate concentration.