Electron Transfer In Cytochrome Research Articles

Electron transfer in cytochrome c. Role of the polypeptide chain

Nuclear magnetic resonance relaxation studies on partially reduced solutions of Candida krusei and horse heart cytochrome c reveal diversity in their functional behavior. Electron transfer between the two oxidation states in vitro proceeds at a rate nearly an order of magnitude slower in Canadida krusei than in the horse heart protein. This difference is interpreted in terms of an active role of the polypeptide chain in the electron transfer process since the hemes in the two proteins are identical in chemical structure and similar electronically. In both cases, electrostatic repulsion between positively charged protein molecules contributes significantly to the observed free energy of activation for the electron transfer process.

A Study of the Mechanism of Electron Transfer in Cytochrome c: CHROMIUM AS A PROBE

Abstract Cytochrome c is swiftly and quantitatively reduced by chromous ion. In the course of the reduction chromium is bound to the protein. At pH 4.78 and 7.0 the ratio of chromium to cytochrome c is approximately 0.5 mole per mole. When phosphate is present during the reduction, the ratio increases to approximately unity, and 1 mole of phosphate is also bound. The chromium-ferrocytochrome c complex can be reoxidized with ferricyanide with little loss of chromium and can be reduced again with dithionite. However, if chromous ion is used to reduce ferricytochrome c-chromium, only partial reduction occurs. The cytochrome c-chromium-phosphate complex is active with cytochrome oxidase and with the cytochrome c reductase of a bovine heart submitochondrial preparation. In the latter system, however, rates are markedly lower. The cytochrome c-chromium-phosphate complex has been digested with pepsin, and a crude fraction has been isolated which still contains iron, chromium, and phosphate.

Vitamins, sugars and ethanol metabolism in man.

IT is generally accepted that the rate-limiting step in the metabolism of alcohol (ethanol) in man is the conversion of alcohol into acetaldehyde1–3. This reaction is believed to occur chiefly in the soluble cytoplasm of liver cells4,5, and is catalysed by alcohol dehydrogenase (ADH)6, NAD acting as hydrogen acceptor7,8. The part played by the interesting ethanol-oxidizing system recently discovered9 in the microsomes of liver cells may be significant, but requires further evaluation. The availability of unreduced NAD in the cell sap seems to be important10,11, because NADH competes with NAD for binding sites on the enzyme ADH and, in sufficient concentration, may inhibit the rate of ethanol dehydrogenation12. The NADH produced in the initial oxidative step in ethanol metabolism must therefore be continually reoxidized by various oxidation-reduction systems for the reaction to proceed13. In the cell sap of liver cells the reoxidation of NADH may be coupled to the reduction of pyruvate to lactate3,8, and to the reductive synthesis14, elongation and saturation of fatty acids; but perhaps the most important route for reoxidation of the NADH involves the mitochondrial flavoprotei–cytochrome electron transfer system coupled with phosphorylating oxidation15–17. The “carrier” of the hydrogen equivalents from NADH across the relatively impermeable mitochondrial membranes may be substances like alpha-glycero-phosphate17, beta-hydroxybutyrate18,19, malate and glutamate20, which serve to “shuttle” hydrogen from the extramitochondrial NADH, across the mitochondrial membranes, for oxidation in the intra-mitochondrial compartment.