Partial purification and characterization of the antidiuretic hormone-inactivating enzyme from renal plasma membranes

An antidiuretic hormone-inactivating peptidase located in renal plasma membranes of porcine kidney medulla has been studied. Treatment of antidiuretic hormone (lysine vasopressin) with renal plasma membranes resulted in a progressive loss of biological activity as measured by the rat pressor assay. The reaction of 2,4,6-trinitrobenzenesulfonic acid with released amino groups was employed to follow the peptidase-catalyzed hydrolysis of the hormone. An 83-fold purification of the membrane-bound peptidase was achieved by Lubrol PX solubilization of the membranes followed by DEAE-cellulose, hydroxylopatite, and 8% agarose column chromatography. The molecular weight of the peptidase was 442 000 as determined by 8% agarose gel filtration. An analysis of the antidiuretic hormone hydrolysis products by thin-layer chromatography revealed the presence of trinitrophenyl-glycinamide. The release of glycinamide from the hormone as a function of time was demonstrated. Mg2+ had a slight inhibitory effect and Ca2+ had a strong inhibitory effect on the peptidase activity.