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Composition and properties of the membrane-bound respiratory chain system of Micrococcus denitrificans

1968; Elsevier BV; Volume: 153; Issue: 2 Linguagem: Inglês

10.1016/0005-2728(68)90081-9

1879-2650

Peter Scholes, Lucile Smith,

Electrochemical sensors and biosensors

1. The respiratory chain system of Micrococcus denitrificans closely resembles that of mammalian mitochondria; it includes cytochromes a + a3, two c-type and at least one b-type cytochrome and DPNH- and succinate dehydrogenases. All of the cytochromes are membrane-bound in preparations from aerobically grown bacteria. Ubiquinone is also localized in the membrane fraction. Although an o-type cytochrome may be present, there is no evidence that it is a functional part of the electron transport chain. The DPNH- and succinoxidase activities show sensitivities to inhibitors entirely similar to those of the mammalian system. 2. The DPNH- and succinate dehydrogenases appear to be distinct entities with different sensitivities to the kind and concentrations of ions in the reaction medium and to inhibition by treatment of membranes with detergent. Both dehydrogenases react with the same cytochrome system, and in most circumstances the dehydrogenases are the rate-limiting steps in the oxidation of the substrates. 3. M. denitrificans can modify the relative amounts of the different cytochromes present according to the conditions of growth; the content of b- and c-type cytochromes is higher and the a-type lower in cells grown anaerobically with nitrate than in cells grown aerobically. The rates of electron transfer are high in cells grown under all conditions tested. There is no evidence that the respiratory chain system is composed of fixed units with precise stoichiometry. 4. The DPNH- and succinoxidase activities of relatively intact membranes are stimulated markedly by freezing and thawing or exposure to sonic oscillation. Detergents can have both stimulatory and inhibitory effects. The data give evidence of the nature of orientation of the respiratory chain pigments on the membrane.