SUBCELLULAR-DISTRIBUTION OF PROTEOLYTIC ACTIVITIES DEGRADING BIOACTIVE PEPTIDES AND ANALOGS IN THE RAT SMALL-INTESTINAL AND COLONIC ENTEROCYTES

The objective of this study was to compare, in rat small intestinal and colonic enterocytes, subcellular distributions of activities degrading the large peptides, neurotensin, acetylneurotensin (8-13), GRF(1-29)NH2 (human growth hormone releasing factor fragment), (desNH(2)Tyr(1),D-Ala(2),Ala(15))GRF(1-29)NH2, Insulin, and insulin B-chain. Proteolytic activities degrading individual peptides in the 10 000-g pellet, rich in intracellular organelles, 27 000-g pellet, rich in brush-border membrane, 100 000-g pellet, and 100 000-g supernatant, rich in cytosol, were determined and compared for both the small intestine and colon. In colonic fractions, the cytosol had highest activity (g protein)(-1) degrading three out of four peptides tested, while in small intestinal fractions, the 27 000-g pellet had the highest activity (g protein)(-1), degrading four out of five peptides tested. In both small intestine and colon, the cytosol had a higher percentage of total proteolytic activity degrading each of the above polypeptides and the highest insulin-degrading activity (g protein)(-1). The results suggest that at pH 7.5, proteolytic activities (g protein)(-1) in the fraction of subcellular organelles are much lower than those in cytosol and that cytosolic proteolytic activities degrading polypeptides and analogues are significant.