Cleavage of oligopeptide p‐nitroanilides attached to N‐(2‐hydroxypropyl)methacrylamide copolymers by guinea pig intestinal enzymes

Abstract

N-(2-Hydroxypropyl)methacrylamide copolymers containing oligopeptide side chains terminated with p-nitroaniline, and low-molecular-weight oligopeptide p-nitroanilides, were synthesized. They were used as substrates to evaluate the enzymatic activity in the gastrointestinal tract of guinea pigs. Brush border membrane enzymes and luminal enzymes (supernatant and pellet) were isolated from guinea pig small intestine and colon, and the cleavage of the substrates was studied in vitro. The results indicate the presence of endopeptidase activity in both small intestine and colon brush border. Phosphoramidon, a potent inhibitor of endopeptidase-24.11, was effective in the cleavage of low-molecular-weight substrates, but ineffective in the cleavage of polymeric substrates, indicating the participation of a different endopeptidase in the cleavage of the latter. Luminal enzymes were more active in the cleavage of polymeric substrates (when compared to low-molecular-weight ones) in accordance with the physiological function of the gastrointestinal tract. The enzymatic activity, both luminal and brush border, was considerably lower in the colon than in the small intestine. This suggests that the colon might be a suitable site for the oral delivery of peptides and proteins.