Fluorescence demonstration of dipeptidyl peptidase II in skeletal, cardiac, and vascular smooth muscles.

Dipeptidyl peptidase II (Dpp II) was demonstrated histochemically in soleus, extensor digitorum longus, cardiac, and vascular smooth muscle tissues using Lys-Ala-4-methoxy-beta-naphthylamide or Lys-Pro-4-methoxy-beta-naphthylamide as the substrate. The enzyme was found to be localized in discrete granules in all muscle types, but varied in its apparent activity. Dpp II activity was greatest in cardiac and least in extensor digitorum longus muscles with activity in soleus and vascular smooth muscles in between these extremes. Since Dpp II is localized only in lysosomes, the relative amounts and locales of lysosomes can be easily observed in normal muscle cells by the techniques described in this study.