On Proteolytic Enzymes X. Tee Enzymes of Papain and Their Activation

The botanist Vines believed that he was able to separate both peptone-forming and peptone-splitting enzymes from the milky sap of Carica papaya (1). Applying quantitative methods to the hydrocyanic acid activation of papain, Willstatter and Grassmann (2) concluded that papain is a homogeneous enzyme. They assumed that hydrocyanic acid plays the role of a kinase that extends the specificity range of the enzyme. According to them, papain converts proteins into peptones and is not able to attack the latter; on the other hand, HCN-papain digests both proteins and peptones. Grassmann later suggested (3) that papain alone is without action on proteins and peptones, and that it requires for the different stages of its activity different specific natural activators. More recent investigators (4,5) have adopted the view that active papain is a sulfhydryl compound which is transformed reversibly into the inactive form by oxidation. This theory has not been extended to include an explanation of the specificity of the enzyme. The experiments to be described in this paper were undertaken to compare the digestion of benzoylisoglutamine, a synthetic substrate (6), with that of peptone from albumin1 In the presence of phenylhydrazine the splitting of the two substrates by HCNpapain was effected quite differently. The hydrolysis of benzoylisoglutamine (Table I) was completely suppressed by modest additions of phenylhydrazine, but peptone digestion was not diminished. As a basis for comparison, the uninhibited enzyme in