Kallikrein and prekallikrein on the basolateral membrane of rat kidney tubules.

Basolateral membrane (BLM) enriched fraction was isolated from homogenized rat kidney cortex by differential centrifugation. We also obtained a fraction enriched in plasma membrane (PM). The morphology of the isolated BLM fragments was studied by transmission and freeze fracture electron microscopy. The relative specific activity of Na+-K+-ATPase was enriched 7-fold, while that of marker enzymes for PM, endoplasmic reticulum, and lysosomes was lower than in the crude homogenate. There was a 10-fold difference in the ratios of activities of Na+-k+-ATPase to Mg2+-ATPase in the BLM and in the PM enriched fractions. Kallikrein activity was determined with S-2266 substrate and by radioimmunoassay of kinin released. It was low in the BLM fraction prior to adding detergent, but Triton X-100 increased the activity 12 to 16-fold. Both free trypsin and Sepharose 4B-bound insoluble trypsin increased kallikrein activity 2- to 3-fold in both the membrane-bound and soluble fractions, probably by activating a prekallikrein. The results were interpreted that the kallikrein studied originated from the distal tubular BLM.