Molecular characterization of human prorenin isoelectric forms

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ObjectiveMammalian renins and prorenins can be fractionated by isoelectric focusing into multiple species, the individual production and decay rates of which vary with certain physiological and pharmacological stimuli. The relative abundance of renin isoelectric species varies in certain pathological states, and the individual species have been reported to differ in their biological function. The present study was undertaken to clarify further the biochemical basis for isoelectric heterogeneity in human renin.DesignPrevious data have suggested that differences in glycosylation contribute to isoelectric heterogeneity in human renin. To determine whether glycosylation was solely responsible for the observed isoelectric heterogeneity, the isoelectric focusing patterns of either native or non-glycosylated human prorenin were compared. The specific activities of the three most abundant isoelectric species of human prorenin were also compared.MethodsTissue culture supernatants from transfected cells expressing either native recombinant human prorenin or human prorenin in which both glycosylation sites were eliminated were fractionated by isoelectric focusing. The expressed prorenins were detected in various fractions by trypsin activation and the angiotensin I generation assay. Specific activities of the various prorenins were estimated by direct comparison of immunoprecipitable radiolabeled prorenin and trypsin-activatable renin activity in the three most abundant fractions.ResultsNative human recombinant prorenin was fractionated into at least five isoelectric species, whereas non-glycosylated human recombinant prorenin migrated as a single isoelectric species, the migration of which was unaffected by forskolin treatment. There was a direct correlation between immunoprecipitable and enzymatically determined prorenin in the three major isoelectric species of native prorenin.ConclusionsThe results suggest that isoelectric heterogeneity of human renin is due solely to differential glycosylation of the protein. The proposed different biological functions of the various isoelectric forms is not directly correlated with variations in their specific activities.

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