[Conversion of proinsulin into insulin in insulin producing tumors in man]

The enzymatic activity of tissues of insulomas and also the proinsulin and insulin content in them was studied. As revealed, insulomas contained an increased amount of proinsulin in comparison with the unaffected islands of Langerhans. The tumours under study also differed by the capacity to catalyze the splitting of hippuryl-L-arginine, synthetic substrate of carboxypeptidase B. Proinsulin content in the tumours of the islar tissue depended on the presence in them of an enzyme catalyzing the splitting of the substrate at pH 6.8--7.2, this pointing to its participation in the conversion of proinsulin into insulin.