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Summary.: Aminoacyl naphthylamidases or aminopeptidases of the rat testicular tissue were fractionated by DEAE-cellulose chromatography and their subcellular site was evaluated by continuous sucrose gradient centrifugation. Four different enzymes were separated with distinct enzymatic properties.
Enzyme I preferentially hydrolysed methionyl-β-NA followed by valyl-, isoleucyl-, leucyl-, phenylalanyl- and alanyl-β-NA at pH 7·0. A slight activation with cysteine and EDTA and a marked inhibition with heavy metal ions was observed. This enzyme was connected to the particles of the mitochondrial—lysosomal fraction. Its main site of function is presumably within the testicular interstitial tissue.
Enzyme II readily hydrolysed a wide variety of substrates with preference for lysyl- and arginyl-β-NA at pH 6·8. It was markedly activated by chelating agents and sensitive to heavy metal ions as well as to some divalent metal ions. This enzyme was tentatively localized in membranous structures and exclusively in the testicular interstitial tissue.
Enzyme III showed the typical characteristics of aminopeptidase B with a marked activation by halide ions. It hydrolysed only arginyl- and lysyl-β-NA optimally at pH 6·5. It is a soluble enzyme and mainly located within the seminiferous tubules.
Enzyme IV showed a large substrate spectrum with optimum at pH 8·0. It was an SH-dependent soluble enzyme. Its main site was within the seminiferous tubules.
None of the four enzymes appear specific for testicular tissue since similar enzymes have been reported in other tissues. Their physiological significance can be evaluated with differential quantification during experimental conditions.
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