50: Peptidases of brush border of human and rabbit small intestinal mucosa

Three peptidase activities were found to be present in human and rabbit small intestinal mucosa: the aminopeptidase A, hydrolyzing the α-L-glutamyl-B-naphthylamide (BNA); the dipeptidyl aminopeptidase IV, hydrolyzing glycyl-L-proline from glycyl-L-prolyl-BNA; a carboxypeptidase, hydrolyzing N-CBZ-L-prolyl-L-alanine. These enzymatic activities are almost totally localized in the brush border and have maximal activity in the distal ileum: they were due to three different enzymes, which have been separated each from the other, as well as from the oligoaminopeptidase (hydrolyzing L-leucyl-BNA), and partially purified. The identification of these new peptidases of the brush border demonstrates a previously unrecognized importance of this subcellular organelle in the digestion of proteins and peptides, in a complementary way to intraluminal and intracellular digestion.