[Enzyme activities of native non-enzymatically glucosylated trypsin, chymotrypsin and papain]

The proteases trypsin, alpha-chymotrypsin and papain were incubated with glucose for a period of 10 days at 37 degrees C and activity was tested in comparison to the enzymes incubated with the puffer solution only without glucose addition. Papain additionally was incubated for 10 days at 37 degrees C with the carbohydrates galactose, sucrose, lactose, glucosamine, galactosamine and mannosamine. While trypsin and chymotrypsin showed no change in enzymatic activity after incubation with glucose, the activity of papain was reduced by 70% to 90% (mean 84%). Incubation with galactose also inhibited papain activity but to a lesser extent (25% to 60%, mean 43%). Incubation with the other carbohydrates failed to inhibit papain activity. The mechanism inferred is nonenzymatic glucosylation of papain possibly as ketoamine linkage at the lysine residues situated close to the active site of papain causing steric or allosteric hindrance of the papain activity. The serine hydrolases trypsin and chymotrypsin without lysine residues near their active sites revealed unchanged activity after incubation with glucose.