Differentiation of trypsin-like enzymes in human plasma.

The arginine amidase and arginine esterase activity of human plasma is compared with that of trypsin, thrombin, plasmin, and kallikrein by using the homologous synthetic amino acid substrates, benzoyl arginine amide (BAA) and benzoyl arginine ethyl ester (BAEE). Hydrolyses of BAA and BAEE in plasma are distinguished by several features: pH optimum, heat stability, storage stability, effect of dilution, surface contact activation, streptokinase activation, inhibition by proteolytic enzyme inhibitor, and range of normal variation. The differential sensitivity of trypsin, throm. bin, plasmin, and kallikrein toward these substrates and the similarity in reaction characteristics of plasma-BAA and trypsin-BAA provide evidence that the arginine amidase activity of plasma represents trypsin, while the arginine esterase activity of plasma is nonspecific.