Isolation and characterization of human brain aminopeptidase which hydrolysis enkephalin-containing peptides

A human brain aminopeptidase, which hydrolyses low molecular weight enkephalin-containing peptides (ECPs), was purified to apparent homogeneity from the homogenate of human brain. The enzyme purification involved DEAE-cellulose chromatography and preparative polyacrylamide gel electrophoresis. The purified aminopeptidase hydrolyses only the Tyr1-Gly2 bond of enkephalines and of ECPs. The rate of hydrolysis of Met-enkephalin and Leu-enkephalin was higher than the rate of hydrolysis of ECPs containing 7 to 13 aminoacid residues. Large ECPs such as peptide E and beta-endorphin were not hydrolysed. The molecular weight of this enzyme is about 100,000 daltons, as determined by gel filtration on Sephadex G-200 and by polyacrylamide gel electrophoresis in presence of sodium dodecyl sulfate. The enzyme has an isoelectric point of pH 4.9, is activated by dithiothreitol (DTT) and inhibited by puromycin, bacitracin, p-mercuryacetate, Zn++, Cu++ and Ni++. The optimum pH for enzyme activity is 7.5.