Effects of inorganic and organic anions on the transport of phosphoenol-pyruvate across the erythrocyte membrane.

Phosphoenolpyruvate is transported across the erythrocyte membrane by a carrier-mediated transport system. The transport of phosphoenolpyruvate was competitively inhibited by inorganic phosphate (Ki = 24 mM) and pyridoxal 5-P (Ki = 0.2 mM), whereas the transport was non-competitively inhibited by L-(+)-lactate (Ki = 37 mM). Specific inhibitors for the inorganic anion transport system such as 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid strongly inhibited the phosphoenolpyruvate transport. Inhibitors for the monocarboxylate transport system, including p-chlormercuribenzoic acid and alpha-cyano-4-hydroxycinnamate, had less inhibitory effects on the phosphoenolpyruvate transport as high as 100 microM. The transport was inhibited irreversibly by treating erythrocytes with pryridoxal 5-P/NaBH4. Transport activities of phosphoenolopyruvate and inorganic phosphate in the treated cells were similarly inhibited depending on the pyridoxal 5-P concentration. The major integral membrane protein, Band 3, was preferentially labelled by treating erythrocytes with pyridoxal 5-P/[3H]-NaBH4. These results suggest that Band 3 mediates the transport of phosphenolopyrvate as well as inorganic phosphate.