Enkephalin inactivation by N-terminal tyrosine cleavage: Purification and partial characterization of a highly specific enzyme from human brain

A soluble enzyme which rapidly degrades both Met and Leu-enkephalin by cleavage of the Tyr-Gly bond has been identified in homogenates of corpora striata from human brain. A marked preference for Met-enkephalin as substrate over Leu-enkephalin was observed. Tyr was not cleaved from other closely related peptides: these include Tyr-Gly-Gly, Tyr-Gly, γ-endorphin, and (d-Ala 2)-Met-enkephalin. Tyr cleavage is catalyzed by a labile, neutral, freeze-sensitive metalloenzyme that is nearly completely inhibited by zinc, bacitracin, puromycin, o-phenanthroline and γ-endorphin. 2-Mercaptoethanol was found to stabilize activity during purification and characterization. This enzyme was purified to homogeneity by chromatography on DEAE-Sephadex and Biogel A 1.5m, and determined to have an apparent molecular weight of 61,500 daltons by SDS-polyacrylamide gel electrophoresis.