Stimulation of Canine Kidney BBMV ATPase Activity by Acidic pH in the Presence of Zn²⁺: An ATPase Activity Distinct from Transport ATPases and Alkaline Phosphatase That May Be an Ecto-ATPase

Abstract

Renal brush border membrane vesicles (BBMV) of the dog possess at least two ATPase activities. In the present study, we have examined the effect of pH, ions, and inhibitors on the activity of ATPase in BBMV. Two different sets of conditions were identified that produced stimulation of ATPase activity. A unique stimulation of BBMV ATPase activity occurred at acidic pH in the presence of 1 mM ZnCl₂. In the absence of Zn²⁺, a second ATPase activity was stimulated by alkaline pH values with peak stimulation occurring between pH 8.5 and 9.0. The results suggest that the alkaline pH-stimulated hydrolysis of ATP probably represents the activity of BBMV alkaline phosphatase. The unique acidic pH + Zn²⁺-stimulated ATPase activity must represent the activity of a second protein other than the alkaline phosphatase, since purified alkaline phosphatase did not show this activity. The biochemical identity and physiological function of this renal BBMV ATPase activity remain to be determined, but it may be an ecto-ATPase

Key Words:

• Zinc
• ATPase
• brush border membrane vesicles
• ecto-ATPase