Separation of Two Dipeptidyl Aminopeptidases in the Human Brain

Soluble dipeptidyl aminopeptidases in the human cerebral cortex were purified by CM‐cellulose, Sephadex G‐200 and hydroxyapatite column chromatography. With hydroxyapatite chromatography two enzymes, dipeptidyl aminopeptidases A and B (DAP‐A and DAP‐B), were separated. DAP‐A and DAP‐B were different from each other in several properties: optimum pH, substrate specificity, K m values in 7‐(Gly‐Pro)‐4‐methylcoumarinamide and molecular weight. They were identified as dipeptidyl aminopeptidases based on the analysis of the products by thin‐layer chromatography. DAP‐A was similar to dipeptidyl aminopeptidase II, but DAP‐B was different from any of the previously described dipeptidyl aminopeptidases (I‐IV) and may be a new dipeptidylaminopeptidase. DAP‐B liberated N‐terminal Arg‐Pro and subsequently Lys‐Pro, from substance P as substrate. Although the physiological roles of these two enzymes in the human brain are not clear yet, they may act on regulation and degradation of biologically active peptides.