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Four aminopeptidases with distinct enzymatic properties in testicular tissue have been found in previous studies (Vanha-Perttula, 1973a). The so-called Enzyme I showed a high specificity for cleaving methionine, isoleucine and valine residues, and resembled an enzyme which has been studied in connection with wound healing (M\l=a"\kinen& Raekallio, 1967, 1968, 1969). Enzyme III appeared to have characteristics similar to those described for aminopeptidase B in many mammalian tissues, with a substrate specificity limited to arginine and lysine residues (Hopsu, M\l=a"\kinen& Glenner, 1966a, b, c). On the basis of biochemical studies, it has been assumed that Enzyme III is located mainly in the seminiferous tubules and Enzyme I in the interstitial tissue (Vanha\x=req-\ Perttula, 1973a, b). Because it is impossible to establish the exact localization of these aminopeptidases in testicular tissue by purely biochemical methods, this investigation was undertaken to determine whether localization could be achieved with a modified azo-coupling histochemical method. The guinea-pig was chosen as the test animal, because previous attempts to demonstrate aminopeptidases histochemically in rat testis have been un¬ successful (Nachlas, Monis, Rosenblatt & Seligman, 1960; Dey & Deb, 1973). Three adult male guinea-pigs were used in the present experiment. The animals were killed by incising the aorta under light ether anaesthesia. The testes were removed by dissection immediately after killing the animals. Samples from the testes of each animal were quickly frozen on dry ice, then attached to a speci¬ men holder using distilled water and cut at 16 μ in a cryostat (Ames, model 4552). The temperature of the cryostat was — 20°C. For the histochemical demonstration of aminopeptidase activity, a semipermeable membranegel combination was used for the incubation of the sections (Huusko, 1974). Because the method is not in common use, it is briefly described. Visking dialysis tubing was cut into 5x5 cm pieces. The pieces were pre¬ pared in 0-05% EDTA solution in order to eliminate impurities and heavy metals present in the membrane and then rinsed in distilled water. Incubation vessels were made by cutting up lengths of glass tubing into sections 2-5 cm in length and 2 cm in diameter. The membrane was stretched over one end of the

THE HISTOCHEMICAL LOCALIZATION OF N-l-ARGINYL-2-NAPHTHYLAMINE- AND N-l-VALYL-2-NAPHTHYLAMINE-CLEAVING ENZYMES IN THE GUINEA-PIG TESTIS