Inhibition of bovine trypsin with human plasma inhibitors

Abstract

Hydrolysis of TAMe (tosyl arginine methyl ester) by trypsin was not inhibited by undiluted plasma or its pseudoglobulin fraction. Dilution of plasma resulted in inhibition of trypsin activity. Inhibition of tryptic hydrolysis of TAMe by urinary trypsin inhibitor (UTI) was prevented by macroglobulin fractions of pseudoglobulin. When case in was used as the substrate a similar phenomenon was not observed because the trypsin- α 2macroglobulin complex does not hydrolyze casein. Highly purified α 2macroglobulin ( α 2M) protected trypsin against other proteinase inhibitors ( α 1antitrypsin or UTI). Mixture of 1.1 μM of α 1antitrypsin ( α 1AT) and 9.1 × 10 −2μM of α 2M did not inhibit 8.3 × 10 −2μM of trypsin significantly, but one tenth amounts of α 1AT (1.1 × 10 −1μM) and 9.1 × 10 −3μM of α 2M showed a large extent of inhibition of 8.3 × 10 −2μM of trypsin. These results may suggest that α 2M rather protected trypsin from its inactivation by other proteinase inhibitors. Such α 2M-trypsin complex still hydrolyzes molecules of certain molecular weights such as tripeptide-pNA (H-D-Val-Leu-Lys-pNA, M.W. 552).