RESUMEN
The molecular weight of NAD-specific isocitrate dehydrogenase, purified from baker's yeast, has been studied by molecular sieve chromatography. By elution of the enzyme from columns of Sepharose 6B with 0.05 M phosphate buffer, pH 7.6, a mol. wt of 151,000 was measured. Higher values of the mol. wt were measured in presence of the following ligands (mol. wt in parentheses): the substrate, isocitrate (224,000); the activators, citrate (203,000) and AMP (275,000); the inhibitor, NaCl (360,000). A mol. wt of 337,000 was measured when AMP, which antagonizes the inhibition by chloride, was present together with NaCl. The results indicate the absence of a correlation between the aggregation form of the enzyme in presence of the ligands and the effects of these ligands on the enzyme activity.
Asunto(s)
Isocitrato Deshidrogenasa , Saccharomyces cerevisiae/enzimología , Adenosina Monofosfato , Cromatografía en Gel/métodos , Citratos , Isocitrato Deshidrogenasa/aislamiento & purificación , Isocitrato Deshidrogenasa/metabolismo , Cinética , Sustancias Macromoleculares , Peso Molecular , NAD , Cloruro de SodioRESUMEN
1. The sensitivity of the NAD(+)-specific isocitrate dehydrogenase from baker's yeast towards inhibition by anions decreases with decrease in pH. The patterns of the pH-dependence of the enzymic activity can be explained by this effect. 2. In the presence of a high isocitrate concentration, citrate, unlike AMP, has no antagonizing effect on the inhibition of the enzyme by anions. In the presence of AMP, citrate inhibits the enzyme at high isocitrate concentration and activates at low isocitrate concentration. 3. The effects on the enzymic activity of the previous incubation of the enzyme were studied in relation to the substrate concentration, the chloride concentration and the presence of citrate and AMP.