Spectrophotometric and kinetic studies of the reconstituted succinate oxidase system

Abstract

Summary Some spectral and kinetic properties of the reconstituted succinate oxidase system of Keilin and King have been studied. 1. With the reconstituted enzyme system the total rate of succinate oxidation was not affected by dilution. 2. The distinct absorption peaks that appeared at 603, 562, 552 and 442 m μ , are essentially the same as those observed for the untreated heart-muscle preparation except for a slight shift of the α -peak of cytochrome a from 604 to 603 m μ . 3. A partial inactivation and/or destruction of the cytochromes may have occurred during the alkali treatment of heart-muscle preparation as indicated by the decrease in the extent of enzymic reduction by succinate as well as their low turnover number. 4. The velocity constants for the sequential reactions of succinate oxidase have been calculated. The magnitudes of these constants are quite similar to those obtained for the untreated heart-muscle preparation. 5. Kinetic evidence indicates that the soluble fraction derived from the alkali treatment of the heart-muscle preparation has a competitive inhibitory effect in relation to the active soluble succinate dehydrogenase (succinate:(acceptor) oxido-reductase, EC 1.3.99.1) on the reduction of cytochrome b by succinate. 6. The molecular relationship between succinate dehydrogenase and cytochrome b as well as the participation of cross-linked respiratory chain assemblies during succinate oxidation are discussed.