A rabbit erythrocyte membrane protein associated with L-lactate transport

Chemical Labeling has been employed to attempt to identify the lactate transport protein of rabbit erythrocytes, which have a very high capacity for stereoselective lactate transport. The lactate transport protein catalyzes lactate/proton cotransport (or lactate/hydroxyl exchange) at physiological pH, as demonstrated by uphill proton fluxes induced by lactate gradients. However, lactate/lactate and lactate/pyruvate exchange are considerably more rapid than lactate/proton cotransport. Although the lactate transporter is less sensitive to inhibition by the stilbenedisulfonate derivative H2DIDS (4,4'diisothiocyano-2,2'-dihydrostilbenedisulfonate) than is the inorganic anion exchanger (band 3), H2DIDS is nonetheless a reasonably potent inhibitor of the lactate transport. A 1-h treatment with 10(-4) M H2DIDS irreversibly inhibits lactate/lactate exchange by greater than 80%. This inhibition appears to be related to the labeling (by [3H]H2DIDS) of an integral membrane polypeptide of Mr = 43,000. This [3H]H2DIDS-labeled polypeptide is absent from human erythrocytes, which have a 100-fold lower Vmax for lactate transport than do rabbit erythrocytes. These experiments suggest that the polypeptide of Mr = 43,000 is a component of the lactate transport system.