[Nature of the enzymes participating in the transformation of proinsulin into insulin]

A study was made of the enzymes of the islands of Langerhans which could participate in the transformation of proinsulin into insulin. The homogenate of the islands of Langerhans of rat and man catalized the hyppuril-L-arginine splitting at pH 5.4-5.8 and 6.8-7.2 which was completely blocked with N-ethyl maleimide. The enzyme of the islands with the optimum action pH of 5.4-5.8 was similar to the enzyme of the exocrine tissue and was possibly a catheptic carboxypeptidase. The second enzyme of the islands differing from the exocrine carboxypeptidase could apparently participate in the insulin formation from the intermediate forms of proinsulin. In the formation of these proinsulin fomrs the participation of the enzyme of the endopeptidase character with a more acid optimum of the action pH is supposed.