Characterization of proteases and protease inhibitors in the rat stomach

The American Journal of Physiology
L NagyS Szabo

Abstract

Previously our laboratory reported increased activity of the thiol proteinase cathepsin B in gastric juice after ethanol-induced mucosal injury. In this study we measured proteinase activity (PA) and proteinase inhibitory activity (PIA) with the general substrates hemoglobin, azocasein, and bovine serum albumin (BSA) at optimal pH (2.0, 5.6, and 7.4) of aspartic, cysteine, and serine proteinases. Homogenates of glandular stomach mucosa and gastric juice from fasted rats were incubated in the presence or absence of specific inhibitors and sulfhydryl (SH) alkylators N-ethylmaleimide and iodoacetate. PIA was measured after acid and heat inactivation of endogenous proteinases and addition of 20 micrograms/ml pepsin, 20 or 100 micrograms/ml thiol proteinase papain, or 20 micrograms/ml trypsin for 5 min before digestion at 37 degrees C. The highest proteolytic activity was found at pH 2.0 (pepsin) in juice and mucosal homogenate, but proteases were also found at pH 5.6 and 7.4, where pepsin was inactive. Pepstatin inhibited most proteolytic activity at pH 2.0. The SH protease inhibitor leupeptin diminished PA mainly at pH 5.6. N-ethylmaleimide or iodoacetate substantially reduced the PA in acidic milieu, with maximum effect at pH 5.6...Continue Reading

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