Fractions highly enriched in plasma membrane, endoplasmic reticulum or brush border were prepared from homogenized rat kidney cortex. Kallikrein was concentrated in the plasma-membrane fraction, but not in the brush border of the proximal tubules. Kininase II or angiotensin I-converting enzyme was localized in the brush-border membrane. It is suggested that kallikrein in the urine may originate from the plasma membrane of the distal tubules and the conversion of angiotensin I and the inactivation of bradykinin may occur on the lumen membrane of the proximal tubular cells.

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