Study of the respiratory chain in Micrococcus luteus (lysodeikticus) by electron‐spin‐resonance spectroscopy

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Abstract
Low-temperature ESR spectroscopy was used to investigate the redox centers of M. luteus membranes. Three different types of Fe-S centers were distinguished. Two of these, a [4Fe-4S]3+-type cluster giving rise to a signal at g = 2.01 in the oxidized state and a [2Fe-2S] cluster with a spectrum at g = 2.03 and 1.93 in the reduced state, were attributable to succinate dehydrogenase. Another, generating signals in the reduced state at g = 2.027, 1.90 and 1.78 was identified as a Rieske Fe-S center. This latter cluster had a mid-point potential (pH 7.0) of +130 mV. In addition, signals characteristic of high-spin ferric heme (g = 6.20), low-spin ferric heme (g = 3.67, 3.36 and 3.01) and Cu2+ (g = 2.18 and 2.02) were also detected. The ferric-heme features, together with the Cu2+ and Rieske centers, were enriched in membrane residues insoluble in Triton X-100, which are known from difference spectroscopy to contain cytochromes b-560, c-550 and a-601 (aa3 oxidase). The signals demonstrated by ESR for M. luteus membranes showed marked similarities to those documented for the complexes II, III and IV of mitochondria. Signals analogous to complex I (NADH-ubiquinone reductase) could not be demonstrated for M. luteus membranes.