The subcellular distribution and storage form of renin in human kidney cortex

An assay with the cation exchange resin Dowex 50 WX2 was developed and validated for the measurement of renin activity in subcellular fractions of kidney cortex. After differential centrifugation, renin was found predominantly in the soluble (SOL) fraction (70%) and to a lesser extent in the heavy mitochondrial (HM) extract (17%). Neither acid pH nor trypsin treatment increased renin activity in these fractions. Discontinuous and continuous sucrose concentration gradients were used to partially resolve renin-containing organelles in the granular moiety from marker enzymes for mitochondria, lysosomes, plasma membranes and peroxisomes. The molecular weight (MW) of renin in both the SOL and HM was approximately 45 000. No acid or trypsin-activatable forms of renin were found after gel filtration of these extracts. When renal cortical tissue was extracted in the presence of the proteolytic enzyme inhibitors N-ethylmaleimide (NEM), ethylenediaminetetraacetic acid (EDTA), aprotinin, phenylmethylsulfonyl fluoride (PMSF), benzamidine and pepstatin, renin activity was not increased by added trypsin. After gel filtration of the homogenates, the MW of renin activity was 45 000. Protease inhibitors did not appear to preserve high molecular weight (HMW) forms and no trypsin-activatable renin was found. These results suggest that in man renal renin is stored within mechanically fragile granules and that the major storage form is of low molecular weight (LMW).