A Protein-Bound Form of Porcine Renal Renin

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Abstract
Two interconvertible renins were isolated from extracts of the pig renal cortex at neutral pH and shown to be protein-bound (renin B, molecular weight 60,000) and free (renin A, molecular weight 40,000) forms of renin. The protein-bound form (renin B) gave a much more prolonged pressor response than did the free form (renin A) on direct bioassay in the rat; it could be converted to renin A by the action of various salts or by acidification below pH 3. The renin-binding protein associated with renin B was isolated by DEAE-cellulose column chromatography under special conditions of elution and appeared to be specific for renin. When pig kidneys were perfused in situ with Krebs-Ringer's solution, isoproterenol stimulation (1-8 µg/min) resulted in release of renin in the protein-bound form. It is suggested that renin-binding protein may act as a carrier for the transport of renin to local tissue sites of uptake under some circumstances and thus alter the mode of expression of the renin-angiotensin system in vivo to one of local angiotensin generation and effect.