Subcellular localization of renin and kininogenase in the rat kidney

1. The distribution of enzymatic activities was determined in subcellular fractions of rat kidney cortex homogenates after various homogenization procedures. The specific activities of kininogenase (KGA), BAEE esterase (pH 8.5), alkaline phosphatase and glucose-6-phosphatase were, on average, 3.4 times higher in the microsomal fraction than in the whole homogenate. The total amount of these activities in the microsomal fraction after gentle, ordinary and forced homogenization were about 15, 40 and 65% of total recovered activities, respectively. These results confirmed the localization of KGA in the microsomal fraction.2. Renin activity was primarily recovered in the heavy mitochondrial fraction. When the force of the homogenization was increased some renin activity was shifted to the soluble fraction.3. When a mixture of renin and purified urinary KGA was given intravenously to an anaesthetized rat, a hypotensive response due to the KGA was followed by a hypertensive renin response. Over a certain range of concentrations KGA and renin could be measured simultaneously. In fractions of kidney homogenates, however, KGA activity was too low to be measured by this method.