Comparative studies on the leucine aminopeptidase activity of different types of leukocytes

The distribution of the leucine aminopeptidase activity among different types of leukocytes in a few animals was examined. In guinea-pig, the enzyme activity was detected in all cell types examined but its activity per cell was diverse among leukocytes, i.e. neutrophils and monocyte-macrophage cell lines, so-called "professional" phagocytes, showed higher enzyme activity than other types of leukocytes, lymphocytes and eosinophils. The same distribution pattern of leucine aminopeptidase activity as that in guinea-pig was also observed among leukocytes in human, rat and mouse. When leukocytes were modified with a poorly permeant reagent, diazotized sulfanilic acid to examine the subcellular localization of leucine aminopeptidase in leukocytes, the leucine aminopeptidase activity of the cells was inhibited by 50% without the inhibition of lactate dehydrogenase, a soluble cytoplasmic enzyme, in various types of leukocytes from all animals used here. The possibility was suggested from these observations that higher leucine aminopeptidase activity is distributed on the cell surface of "professional" phagocytes.