Participation of alkaline phosphatase in the active transport of phosphates in brush border membrane vesicles

Abstract

Hamster and rat kidney brush border membrane vesicles were compared for their ability to transport phosphate in vitro . In presence of 0.1 mM inorganic phosphate, the Na + dependent uptake was greater in rat than in hamster but the Km values for uptake were respectively 0.32 mM and 0.12 mM for hamster and rat. In presence of glycerophosphate, as sole source of phosphate, only hydrolysed phosphate was transported but in a much greater amount (× 10) than the one expected from the actual concentration of inorganic phosphate released by the action of alkaline phosphatase during the course of the experiments. Although the Na + dependent uptake of phosphate from glycerophosphate relied on alkaline phosphatase action, the extent of transport did not seem to be correlated to the amount of catalytic activity present, pointing to a concerted action between alkaline phosphatase and the phosphate carrier.