Cytochemical localization and biochemical characterization of dipeptidyl aminopeptidase II in macrophages and mast cells.

Dipeptidyl aminopeptidase II (DAP II) was demonstrated cytochemically at light and electron microscope levels in rat macrophages and mast cells using Lys-Ala-4-methoxy-2-naphthylamide as a specific substrate. The enzyme which was found to be lysosomal in both cell types, was analyzed biochemically in extracts by measuring fluorometrically the liberated naphthylamine, and was visualized in sections microscopically using azo-coupling methods. DAP II was further characterized by isoelectric focusing techniques. Macrophage DAP II was found to be typical of that found in other rat tissues in terms of its structural latency, substrate specificity, inhibitor sensitivities, and pH activator requirements. Addition DAP II isozymes, not previously recognized, were observed.