Leucine aminopeptidase and ferricyanide reductase activities in radish microsomes

A NADH-ferricyanide reductase activity found in radish microsomes isolated from germinated seeds has been shown to be stimulated by pCMB and pCMBS which are both strong nactivators of many plant proteolytic enzymes. In the same preparation a leucine aminopeptidase was found while endoprotease and carboxypeptidase activities were not detected using exogenous substrates. The aminopeptidase, highly active at the same optimal pH-condition of FeCN reductase, was stimulated by CoCl₂ and non-polar detergents (Triton X-100 and Brij 35). It was inhibited by sulphydryl reagents. By gel filtration of microsomal detergent extract two peaks of activity were separated: red I coeluted with LeuAPase and red II, free of aminopeptidase. Red I, a protein, was inhibited by sulphydral reagents and stimulated by duroquinone. Red II, stimulated by pCMB, is not a protein because of the small size and the noninfluence of heating treatment on catalytic activity.