The nature of papain

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Abstract
Preps. of papain obtained by completely oxidizing the SH groups of natural papain by H2O2 or alloxan, while retaining the property of hydrolysing gelatin or egg albumin, were inactive towards Witte''s peptone. Roche peptone. silk peptone and hippuryl-amide. The optimum pH for gelatin hydrolysis by SS-papain was 3.6-3.8, by SH papain the optimum pH was spread over the range pH 3-5. The activation of SH papain by cyanide, cysteine or glutathione extended the range of specificity. Maleic acid inhibited the hydrolysis of peptone by SH papain, while it was without effect on gelatinase. These considerations led to the view that the SH group was not essential for gelatinase activity, but was necessary for the peptonase activity: another group which reacted irreversibly with iodoacetic acid was essential for both the gelatinase and peptonase activities.