The existence of a membrane-bound HCO3-stimulated ATPase in intestinal mucosa is controversial. A crude brush border fraction of rat small intestinal homogenates contained HCO3-ATPase activity which was inhibited by preincubation with 3 mM EDTA. Alkaline phosphatase activity of this preparation was also inhibited in a parallel, time-dependent fashion by preincubation with EDTA. When 5 mM ZnSO4 accompanied 3 mM EDTA in the preincubation mix, preservation of both enzyme activities occurred, demonstrating a requirement of Zn for the activity of both these phosphatases. These studies support the earlier contention that HCO3-ATPase and alkaline phosphatase activities may be different properties of the same enzyme, and raise the possibility that the ATPase could play a role in intestinal ion transport. The failure to identify a membrane-bound HCO3-ATPase by other workers could be due to the exposure of EDTA which occurred in their tissue preparation.

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