Effect of bile acids and pH on the release of enteropeptidase in man

Bile acids increase the release of human enteropeptidase as well as other brush-border enzymes (alkaline phosphatase, leucine aminopeptidase) from duodenal mucosa, as had been shown earlier in experimental animals. The action of bile acids is independent of their known enhancing effect on enteropeptidase activity. The pH of duodenal juice is an important, hitherto unrecognized, factor in the release mechanism of brush-border enzymes. All of the above enzymes tested were released to a markedly greater extent at pH 8.2 than 6.3, regardless of the presence or absence of bile acid. Contrary to some results obtained with animal tissue, by other investigators, our experiments with human duodenal mucosa indicate that enteropeptidase, under all conditions tested, is released at a rate considerably greater than that for alkaline phosphatase or leucine aminopeptidase. The looser association of enteropeptidase with cellular components relative to that of other brush-border enzymes, as indicated by our observations, may be related to the unique function of enteropeptidase as the trigger enzyme of protein digestion.