Effect of the X-linked Hyp mutation on N-ethylmaleimide labelling of proteins in renal brush border membrane.

The X-linked dominant mutation, hypophosphataemia (gene symbol, Hyp) is expressed in the laboratory mouse as deficient phosphate transport at the renal brush border membrane (BBM) of proximal nephron. In an attempt to identify proteins which mediate phosphate transport, we treated renal BBM vesicles prepared from mutant male (Hyp/Y) and normal male (+/Y) littermates, with radiolabelled N-ethylmaleimide (NEM), in the presence or absence of arsenate of arsenate which is a competitive inhibitor of phosphate transport. Polyacrylamide gel electrophoresis revealed labelling of membrane proteins in the 40-45 kDa range; addition of arsenate during NEM treatment inhibited labelling. These findings indicate a 40-45 kDa protein as a component of the renal BBM phosphate transport system(s). We found no difference between protein labelling of the renal BBM from Hyp/Y and +/Y mice.