Studies on the characterization of isolated renin-containing granules: the storage form of renin

Renin-containing granules isolated by isopycnic zonal centrifugation were partially characterized biochemically. Extracts of the granules were found to have a dual pH optimum at 5.5-6.0 and 7.0-7.5 and possess linear time-dependence of product formation when reacted with homologous renin substrate. Extracts also possessed a first order reaction constant of 0.713 X 10(-2). Treatment of the extracts with ammonium sulfate increased the velocity of the renin/renin substrate reaction though it continued to be linear with respect to time. This partially purified renin preparation was found to have a Km=3.9 X 10(3) ng/ml. Gel filtration of this preparation of renin demonstrated the presence of an active protein with renin activity and a molecular weight of 59,000 daltons in addition to an inactive protein of molecular weight 13, 750 daltons which may be a potential inhibitor of the renin/renin substrate reaction. The former protein or "big renin" may be the storage form or porhormone state of renin within the renin-containing granules of the juxtaglomerular cells.