Leucine aminopeptidase as an echo-enzyme of polymorphonuclear neutrophils

Intact polymorphonuclear neutrophils were modified chemically by a poorly permeable reagent, diazotized sulfanilic acid, and the changes in the activity of 5'-nucleotidase, alkaline phosphodiesterase, and leucine aminopeptidase were examined. Among three plasma membrane enzymes, 5'-nucleotidase activity was hardly detected in the human neutrophils. The activity of alkaline phosphodiesterase was observed in all the neutrophils examined, but was not inhibited by diazotized sulfanilic acid in the guinea-pig neutrophils. On the other hand, the activity of leucine aminopeptidase was not only found but also inhibited by diazotized sulfanilic acid without the inhibition of lactate dehydrogenase, a cytosol enzyme, in all the neutrophils, suggesting that leucine aminopeptidase is located generally on the plasma membrane as an ecto-enzyme in the neutrophils.