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PubMed1981

Characterization of the potentiometric behavior of soluble cytochrome oxidase by magnetic circular dichroism. Evidence in support of heme-heme interaction.

Magnetic circular dichroism spectroscopy has been used to characterize the oxidation-reduction behavior of cytochromes a and a3 during potentiometric experiments. The experiments were complicated by the presence of slow, time-dependent changes during reduction, and it appears that reliable results can only be obtained during reoxidation or with enzyme that has been subjected to a cycle of reduction and oxidation. Under all experimental conditions the reduction levels of cytochrome a and a3 are comparable. This result cannot be reconciled with a model in which the two heme centers have defined and well resolved potentials. The most straightforward explanation of the data requires an oxidation-reduction coupling of the potentials of the two hemes, i.e. an allosteric or heme-heme interaction, which is about 2 K cal/mol in magnitude. There is a good correlation between magnetic circular dichroism and EPR measurements obtained on parallel samples. The kinetics of the slow, time-dependent processes have been characterized by measurement of a variety of spectral properties and enzyme activity. All parameters measured change at comparable rates, implying a common rate-controlling event. A new copper EPR signal has been observed at high pH. This signal appears to rise from the "EPR-undetectable" copper center.

Animals↗
PubMed2001

Methylobacillus flagellatus KT contains a novel cbo-type cytochrome oxidase.

The o-type oxidase from the methanol-grown obligate methylotroph Methylobacillus flagellatus KT has been purified to homogeneity. The complex is composed of four subunits (57, 40, 35 and 30 kDa). It contains six haems (4C:1B:1O) and one copper atom per molecule. It is proposed that the haem O-Cu(B) binuclear centre and a low-spin haem B are located in subunit I (57 kDa), two haems C reside in the cytochrome c homodimer (35 kDa), two haems C belong to the dihaem cytochrome c (30 kDa). The presented data provide evidence that cytochrome cbo is a novel representative of the haem-copper oxidase superfamily.

Chromatography, High Pressure Liquid↗