Aminopeptidases in seeds of Picea abies (L.) karst.: Characterization of leucine aminopeptidase by molecular properties and inhibitors

By either acrylamide or starch gel electrophoresis of Norway spruce (Picea abies) seed extracts, two prominent isoenzyme bands were obtained after staining for leucine aminopeptidase (LAP). These bands were proved to correspond to each other by reelectrophoresis in both gel media. Single endosperm studies with acrylamide gels showed clearly that, in addition to LAP, two bands are expressed after staining for alanine aminopeptidase (AAP) as well. Both the LAP and the AAP activities appeared together as a single peak between catalase and ferritin after gel chromatography on Sepharose. Isoelectric focusing in sucrose gradients proved the two LAP activities to have identical isoelectric points and revealed that LAP, but not AAP, is detectable by standard starch gel electrophoretic procedures. The two LAP bands refer to approximate molecular weights of 71,000 and 131,000, respectively. Disaggregation studies did not conclusively determine whether these two bands represent different enzymes or not. Only inhibitors succeeded in producing a definite differentiation by selective inhibition of one of the two bands. It is concluded that in both gel media the isoenzyme bands reflect the activity of two distinct leucine aminopeptidases.