Abstract
Rat kidney contains membrane-bound renin (EC 3.4.99.19) and kallikrein (EC 3.4.21.8). Kallikrein activity was measured by a spectrophotometric assay and renin by radioimmunoassay. Plasma membrane-bound kallikrein was activated by lysolecithin and by melittin, which was a more potent activator., This activation by mellitin was independent of calcium concentration. Mellitin was, however, a more potent activator of membrane-bound renin in the presence of calcium. Administration of aldosterone to rats for 6 days increased kallikrein activity in the renal homogenate and in the membrane-enriched fractions, whereas renin activity was not affected. It was proposed that kallikrein may also be located on the basal membrane of tubular epithelial cells, where aldosterone can enhance its activity.