Membrane polypeptide in rabbit erythrocytes associated with the inhibition of L-lactate transport by a synthetic anhydride of lactic acid

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Abstract
The synthetic lactyl anhydride isobutylcarbonyl lactyl anhydride (iBCLA), a selective and potent inhibitor of L-(+)-lactate transport in rabbit erythrocytes, reduces the chemical labeling of a 40-50-kdalton polypeptide by 3H 4,4''-diisothiocyanatodihydrostilbene-2,2''-disulfonate ([3H]H2DIDS). iBCLA does so in a dose-dependent manner at concentrations that strongly inhibit lactate exchange but not chloride-phosphate exchange. These labeling experiments and inhibition reversal studies using iBCLA, p-(chloromercuri)benzenesulfonic acid (pCMBS), and dithiothreitol (DTT) suggest that iBCLA does not act at SH groups but at or near an amino group that is near a disulfide linkage in the polypeptide which catalyzes lactate transport. These experiments support the association between specific monocarboxylate transport and a 40-50-kdalton membrane-bound polypeptide of the rabbit erythrocyte.