Aminopeptidases of Rat Testis

Summary. The lysosomal enzymes, dipeptidyl Aminopeptidase I and II, were found in rat testicular tissue. Enzyme I hydrolysed seryltyrosyl-β-naphthylamide (Ser-Tyr-β-NA) optimally at pH 4·5 and was activated by thiol-groups and chloride ions. Enzyme II had a model substrate of Lys-Ala-β-NA, which was optimally hydrolysed at pH 5·5. These enzymes were partially separated by DEAE-cellulose chromatography. The major activity of Enzyme I appeared to be in the interstitial tissue, since isolated seminiferous tubules contained only trace amounts of this activity. By contrast, Enzyme II appeared to be present in both the interstitial and tubular tissues. During the pubertal maturation of the testis, a gradual increase in Enzyme I activity was observed. Cryptorchidism caused an initial suppression in 5 days, followed by a rapid increase. These findings indicate a functional correlation of Enzyme I activity with the Leydig cells. Enzyme II activity showed only a slight decrease during puberty. After cryptorchidism, an initial increase was encountered at 5 to 8 days, followed by a rapid decline. These observations further indicate the presence of this enzyme in both the interstitial and tubular tissues. Cadmium chloride treatment caused an initial increase of Enzyme I activity which was coincidental with the rapid destruction of the seminiferous epithelium. Subsequently, a decline followed which was concurrent with the destruction of the interstitial cells. Enzyme II showed a more rapid suppression soon after cadmium chloride treatment.