| Abstract: | The kinetics of pyruvate transport across the isolated red blood cell membrane were studied by a simple and precise spectrophotometric method: following the oxidation of NADH via lactate dehydrogenase trapped within resealed ghosts. The initial rate of pyruvate entry was linear. Influx was limited by saturation at high pyruvate concentration. Pyruvate influx was greatly stimulated by increasing ionic strength in the outer but not the inner aqueous compartment. The Km ranged from 15.0 mM at mu = 0.05 to 3.7 mM at mu = 0.01, while the V went from 0.611 - 10(15) to 0.137 - 10(-15) mol - min-1 - ghost-1. Ionic strength was shown to affect the translocation step and not pyruvate binding. The energy of activation of pyruvate flux into resealed ghosts was 25 kcal/mol, similar to that found in intact red blood cells. Inhibitors of pyruvate influx included such anions as thiocyanate, chloride, bicarbonate, alpha-cyanocinnamate, salicylate and ketomalonate (but not acetate); noncompetitive inhibitors were phloretin, 1-fluoro-2,4-dinitrobenzene, 4-acetamido-4'-isothiocyanate-stilbene-2,2'-disulfonic acid and o-phenanthroline/CuSO4 mixtures. The last reagent, known to induce disulfide links in certain membrane proteins, blocked the ionic strength stimulation of pyruvate influx in this study. |
