Peptide hydrolases of the human small intestinal mucosa: identification of six distinct enzymes in the brush border membrane.

For this investigation highly purified brush border membranes from human small intestine, prepared according to the method described in the preceding paper [1], have been used. Solubilisation of brush border membrane proteins by sodium dodecyl sulphate, Triton X-100 and papain followed by electrophoresis in polyacrylamide gels revealed six distinct peptide hydrolases. These included the enzymes aminopeptidase A (EC 3.4.11.7), dipeptidylpeptidase IV (EC 3.4.14.-), gamma-glutamultranspeptidase (EC 2.3.2.2) and aminopeptidase M (EC 3.4.11.2), which were clearly separable on polyacrylamide gels after solubilisation with Triton X-100 or papain. Activity recovered in the aminopeptidase M peak in the above gel system could be resolved into two distinct peptidases in addition to aminopeptidase M, by SDS-gel-electrophoresis. One of these peptidases was most active towards aliphatic tripeptide (aminopeptidase 1) while the other appeared to be specific for dipeptides (aminopeptidase 2).