Erepsin

EREPSIN, an enzyme system contained in the intestinal juice that completes the full digestion of proteins in the digestive tract. For a long time, erepsin was viewed as a single enzyme incapable of acting on native, undigested proteins, but hydrolyzing deeper protein breakdown products—polypeptides—into the individual amino acids that compose them. Detailed analysis using improved modern adsorption methods of studying enzymes has shown, however, that the intestinal juice contains not a single universal enzyme hydrolyzing polypeptides, but a more complex complex of such enzymes (peptidases or ereptases). This complex includes: dipeptidase, an enzyme that splits only dipeptides and does not act on more complex peptide chains; among dipeptides, derivatives of the amino acid proline resist the action of this enzyme and are apparently split by a special enzyme, prolinase. The second and most important component of erepsin is a m i n o - p o l y p e p t i d a s e, which does not act on dipeptides and hydrolyzes complex polypeptides. Here, the action is directed at the amino acid of the peptide chain that stands at its end and bears a free amino group; the substitution of this group makes the peptide inaccessible to the action of amino-polypeptidase. The optimum action of this enzyme lies around pH = 7.0. Under the action of amino-polypeptidase, the peptide chain is gradually shortened, each time by one amino acid residue, and upon reaching the dipeptide stage, dipeptidase comes into action. Less reliable can be considered the established presence in the composition of erepsin of the so-called carboxy-polypeptidase, an enzyme that cleaves from the peptide the amino acid that has retained a free carboxyl. Natural intestinal contents, even in sections remote from the duodenum, as a rule also contain agents capable of acting on native proteins, i.e., proteinases. However, they apparently originate from pancreatic juice, since in pure intestinal juice from an intestinal loop their content is negligible or they are entirely absent. A comparative study of intestinal mucosa enzymes and leukocyte enzymes led Willstätter to the idea that leukocytes migrating into the cavity of the intestinal canal might play a significant role as a source of intestinal erepsin. This assumption, however, still needs verification. The individual components of erepsin do not represent any special enzymes specific only to the intestinal juice. They turn out to be widely distributed in the animal organism. They are contained—in different quantitative ratios—in pancreatic juice, as well as in almost all organs and tissues.