The capacity of ileal mucosal cell membranes to effect phosphate release was examined. In the presence of optimal concentrations of adenosine triphosphate or guanosine triphosphate and magnesium, cholera toxin rapidly enhanced the release of phosphate; a lag or slow activation period was not observed. The enhancement of phosphate release by cholera toxin was dose-dependent, and did not appear to involve an increased utilization of adenosine triphosphate. The release of phosphate by cell membranes was stable for 4 weeks when stored at -80°C. The use of effectors to modify enzymatic activities in cell membrane preparations suggested that membrane bound adenylate cyclase and adenosine triphosphatase were not essential for phosphate release.
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