LEUCINE AMINOPEPTIDASE - A ZINC METALLOENYZME

The leucine aminopeptidase of the supernatant fraction of porcine kidney is instantaneously inhibited by orthophenanthroline, bipyridyl, cupferron, sodium diethyldithiocarbamide, sodium sulfide, and sodium cyanide. All of these inhibitions are reversed by addition of group IIb metal ions in appropriate quantity to the reaction mixture. During purification of the enzyme under conditions which minimize the addition of extraneous metal, the zinc-to-protein ratio in the fractions rises to a final value between 4 and 6 g-atoms per 300,000 g of protein, as estimated by three independent analytical methods, while the content of all other metals falls to negligible levels. Removal of the zinc from the purified enzyme or its replacement by cadmium results in loss of enzyme activity in proportion to the loss of zinc. Replacement of the cadmium in cadmium leucine aminopeptidase by zinc restores native levels of activity. Manganese can also partially replace the zinc of the purified enzyme yielding a derivative more active toward both leucine amide and leucine p-nitroanilide than the native enzyme. These data suggest that leucine aminopeptidase is a zinc metalloenzyme. © 1969.