L(-LACTATE BINDING TO A PROTEIN IN RAT SKELETAL-MUSCLE PLASMA-MEMBRANES())

Biochemical studies were conducted to determine the location of a puta tive lactate transport protein in rat skeletal muscle plasma membranes (PM). PM (50-100 mu g protein) were incubated with [U-C-14] L(+)-lact ate, in the presence or absence of unlabeled monocarboxylates or poten tial inhibitors, after which proteins were separated by SDS-PAGE. Gel slices (2 mm) were cut and analyzed for C-14. [U-C-14] L(+)-lactate wa s bound to plasma membranes in the 30 to 40 kDa molecular mass range. Binding of [U-C-14] L(+)-lactate was inhibited by N-ethylmaleimide, un labeled L-lactate and pyruvate, and in a dose dependent manner by alph a-cyano-4-hydroxycinnamate (r = 0.995), but not by cytochalasin-B. The inhibition of [U-C-14] L(+)-lactate binding was similar, to the inhib ition of lactate transport. Therefore the transport of L(+)-lactate ac ross skeletal muscle plasma membranes involves a polypeptide of 30 to 40 kDa.