Assuntos
Ácido Aspártico/metabolismo , Glutamatos/metabolismo , Mitocôndrias Hepáticas/metabolismo , Acetatos/farmacologia , Animais , Transporte Biológico/efeitos dos fármacos , Cálcio/farmacologia , Concentração de Íons de Hidrogênio , Cinética , Masculino , Matemática , Potenciais da Membrana , Mitocôndrias Hepáticas/efeitos dos fármacos , Nigericina/farmacologia , Ratos , Valinomicina/farmacologiaAssuntos
Ácido Aspártico/metabolismo , Transporte Biológico , Glutamatos/metabolismo , Mitocôndrias Hepáticas/metabolismo , Animais , Computadores , Cinética , Matemática , Mitocôndrias/metabolismo , Dilatação Mitocondrial , NAD/metabolismo , NADP/metabolismo , Oxirredução , Consumo de Oxigênio , RatosRESUMO
Activation of membrane-associated thiamin triphosphatase from rat brain requires a divalent cation (Mg2+, Ca2+, or Mn2+). The optimum concentration of Mg2+ necessary for maximal enzyme activity varies with substrate concentration; conversely, the maximal rate of hydrolysis attainbale by increasing thiamin triphosphate concentration is directly proportional to [Mg2+] for all levels of Mg2+ below that of the substrate. Under appropriate conditions, the Km of the thiamin triphosphatase for Mg2+ and for thiamin triphosphate are shown to be identical. Dissociation constants (Kd) for the binding of Mg2+ to thiamin triphosphate, thiamin diphosphate, and thiamin were determined; kinetic data re-expressed in terms of [Mg2+-thiamin triphosphate] conform to simple single substrate predictions, suggesting that the true enzyme substrate may be the Mg2+-thiamin triphosphate complex. Excess free Mg2+ inhibits thiamin triphosphatase activity competitively while excess free thiamin triphosphate in concentrations up to 10 times Km has no effect on the membrane-bound enzyme.