Glycylglycylphenylalaninamide synthesis catalysed by papain in a medium containing polyols

The influence of several polyols (ethylene glycol, glycerol, erythritol, xylitol and sorbitol) on both the thermostability and tripeptide(Gly-Gly-PheNH2)-synthesis capability of papain was studied at 60 degrees C. The results obtained from the thermostability studies on papain showed that polyols increased the half-life time of the esterase activity of the enzyme proportionally to their molecular size and concentration, except for ethylene glycol. The presence of polyols, as water-activity-depressing agents, also enhanced the enzyme activity for Gly-Gly-PheNH2 synthesis in a way which was directly proportional to the molecular size of the polyol molecule and its water-activity-depressing power. A linear relationship between the increase in the synthetic/hydrolytic activity ratio and the overall concentration of hydroxy groups in the reaction media was obtained, indicating that these latter groups are mainly responsible for the modification of the catalytic behaviour of the enzyme, as a result of a change in their microenvironment.