Demonstration of Renin Activity in Purified Rat Leydig Cells: Evidence for the Existence of an Endogenous Inactive (Latent) Form of Enzyme*

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Abstract
Previous histochemical studies demonstrated the specific localization of an immunoreactive, renin-like substance in Leydig cells of rat testes. A specific renin enzyme activity in the 2 purified populations of Leydig cells (I and II) of mature rat testes was demonstrated. Leydig cells of both populations also exhibited an inactive (latent) renin, which was activated by the sulfhydryl reagents dithiothreitol, .beta.-mercaptoethanol, glutathione, and cysteine, but not by limited proteolysis by trypsin, which is a characteristic activating agent for prorenin or inactive renin of the zymogen type. The activation of latent renin by dithiothreitol produced .apprx. 5- and 10-fold increases in renin activity in Leydig cell populations I and II, respectively. Active and latent renin showed strong affinity to an antirat renin immunoglobulin-Sepharose column, indicating a close immunological relationship of latent renin to active renin. Both active and latent renin from Leydig cell populations (I and II) exhibited the pH optimum of 6.0. The gel filtration of Leydig cell extracts characteristically revealed that the apparent MW of active and latent renin were 39,000 and 48,000, respectively. Both active and latent renin in Leydig cells remained almost at similar levels through 4 continuous subcultures. The activity of latent renin slightly increased during the 4 consecutive subcultures, while active renin levels remained almost constant.