Histochemical method for dipeptidyl aminopeptidase II with a new anthraquinonyl hydrazide substrate

A new method for the histochemical visualization of lysosomal aminopeptidas e dipeptidyl peplidase II activity (DPP II) is developed. The substrate L-L ys-L-Ala-5-chloro-1-anthraquinonylhydrazide-2HBr (Lys-Ala-CAH) is readily h ydrolyzed by the enzyme to release 5-Cl-1-anthraquinonyIhydrazine (CAH). Th e last compound is simultaneously coupled to an aromatic aldehyde, e.g 4-ni trobenzaldehyde (p-NBA) or piperonal (3,4-methylenedioxybenzaldehyde; PPL), to form a highly insoluble deeply colored hydrazone, marking the enzyme lo cations. Using the new method, DPP II is successfully localyzed in tissue s ections from different rat organs.