Purification and characterization of enkephalin-degradating enzymes from calf-brain striatum

Enkephalinase A and B are extracted from Triton-X 100 washed calf-brain particles and purified by DEAE-cellulose chromatography. Both enzymes have identical Km values in their membrane-bound and soluble form. Enkephalinase A has a pH optimum at 6.9 and a Km for Leu-enkephalin of 20-25 microM, which hardly depends on the pH. Thiorphan and phosphate are purely competitive inhibitors of Enkephalinase A with Ki values of 3 nM and 1.5 mM respectively (pH = 6.85). Enkephalinase B is not affected by phosphate or thiorphan. It has a Km for Leu-enkephalin of 10 microM, a pH optimum of 7.0 and is inhibited by low concentrations of apolar dipeptides.