Phosphate-binding proteolipid from brush border

A proteolipid that binds inorganic phosphate with high affinity and specificity has been extracted from rabbit kidney brush-border membranes. This proteolipid has been partially purified by chromatography on LH-20. The molecular weight of the proteolipid is approximately 3000 as determined by urea-sodium dodecyl sulfate gel electrophoresis. This proteolipid can bind and transport phosphate into an organic phase. The K0.5 for phosphate binding is 8 microM with a Hill coefficient of 1.92. Arsenate inhibits phosphate binding in a competitive manner with a KI of 27.5 microM. The aminoreactive reagent 2,4-dinitrofluorobenzene inhibits phosphate binding to the proteolipid. Similarly, 2,4-dinitrofluorobenzene inhibited Na+-driven Pi uptake in renal brush-border membrane vesicles. In contrast to the mitochondrial phosphate binder, this proteolipid is not inhibited by sulfhydryl reagents. We suggest that this molecular species is a likely candidate for involvement in phosphate uptake in the renal tubule.