A new one-step method for light and electron microscopic localization of the K-dependent phosphatase (K-NPPase) component of the Na-K-ATPase complex was applied to the rat kidney. In the cortex, intense K-NPPase reaction was localized to the distal convoluted tubules and collecting tubules. Proximal convoluted tubules, especially the first segment, showed weak activity. In the medulla, thick ascending segments of the Henle's loop showed high activity, while thin segments never showed activity.

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... he reaction products of K-NPPase activity were localized on the cytoplasmic side of the lateral and basal plasma membranes of the renal tubular epithelium, indicating the direction of the phosphate liberation by the enzyme to be the cytoplasmic side. The above results were discussed with special reference to the renal physiological function.