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Papain contains a cysteine-activatable proteinase that hydrolyzes benzoyll-arginlneamide (1). This enzyme has been shown to have a specificity similar to that of crystalline pancreatic trypsin (2) and therefore has been designated papain trypsinase (3). Previous experiments have shown that papain trypsinase exists in two inactive forms which can be designated papain-a-trypsinase and papain-13-trypsinase (4). Only the 13-trypsinase can be activated by HCN. However, a-trypsinase can be transformed into the 13-form by minute amounts of sulfhydryl compounds such as H~S or cysteine. The activation of the 0-form by an excess of HCN or H~S is completely reversed when the activator is removed in vacuo. These results have been interpreted to indicate that the reversible activation of papain-fl-trypsinase consists in the formation of dissociable activator-13-trypsinase compounds, as represented below.

The process of the gastrointestinal digestion of food proteins is generally assumed to involve only the breakdown of the proteins into amino acids.Thus peptic and tryptic proteinases are supposed to perform exclusively hydrolytic reactions under the physicochemical conditions prevalent during digestion.Recent experiments (1, 2) have shown that the intracellular proteinases papain, cathepsin, and bromelin are capable of synthesizing hippurylanilide from hippuric acid and aniline and also benzoyl-l-phenylalanyl-Lleucine anilide from benzoyl-l-phenylalanine and kleucine anilide.It has now been observed that a preparation of crystalline chymotrypsin effects the synthesis of benzoyl-Ltyrosylglycine anilide from benzoyl-Z-tyrosine and glytine anilide.