Cytochrome b subunit

It is known that protein kinase C can phosphorylate a number of key oxidase components, such as the two cytochrome b subunits and the 47-kDa cytoplasmic factor. This process is prevented by protein kinase C inhibitors such as staurosporine (although it is now recognised that this inhibitor is not specific for protein kinase C), which also inhibits the respiratory burst activated by agonists such as PMA. However, when cells are stimulated by fMet-Leu-Phe, translocation of pAl-phox to the plasma membrane can occur even if protein kinase C activity is blocked - that is, phosphorylation is not essential for the translocation of this component in response to stimulation by this agonist. Similarly, the kinetics of phosphorylation of the cytochrome subunits do not follow the kinetics of oxidase activation, and protein kinase C inhibitors have no effect on oxidase activity elicited by some agonists -for example, on the initiation of the respiratory burst elicited by agonists such as fMet-Leu-Phe (Fig. 6.14). Furthermore, the kinetics of DAG accumulation do not always follow those of oxidase activity. Hence, whilst protein kinase C is undoubtedly involved in oxidase activation by some agonists, oxidase function is not totally dependent upon the activity of this kinase. 

In mid-2006, a search of the Jena Library for cytochrome b returned 197 entries, including those described in Sections 7.5 (cytochrome bef) and 7.6 (cytochrome bci). Cytochrome b contains the heme b subunit (heme protoporphyrin IX), the same metal cofactor contained in hemoglobin and myoglobin (see Figure 7.1). Other cytochrome b subunits occur in the cytochrome bef complex, also known as plasotquinol iplastocyanin reductase (EC 1.10.22) and... 

The site of menaquinol oxidation on the diheme cytochrome b subunit of W. succinogenes QFR is not known. No convincing density for... 

Brasseur, G., Saribas, A. S., and Daldal F., 1996, A Compilation of mutations located in the Cytochrome b Subunit of the Bacterial and Mitochondrial bcl Complex, Biochim. Biophys. Acta 1275 61n69. 

Hacker, B., Barquera, B., Crofts, A. R., and Gennis, R. B., 1993, Characterization of mutations in the cytochrome b subunit of the bcl complex of Rhodobacter sphaeroides that affect the quinone reductase site (Qc), Biochemistry 32 4403n4410. 

Nitric oxide reductase cytochrome b subunit Nitrous oxide reductase... 

The active form of selenium in M. vannielii has been identified as occurring as selenocysteine residues . In addition to selenium, the known selenium-dependent formate dehydrogenases contain molybdenum and iron-sulfur centers. The E. coli enzyme also contains cytochrome b subunits . It has been characterized as an approximately... 

On the other hand, the mitochondrial genome is believed to code for the largest polypeptide of cytochrome oxidase, an enzyme that has been highly purified and has been found to be composed of seven subunits. When the enzyme is placed on polyacrylamide gel, the exact molecular weight of the subunits is not known, but it is believed to range between 8,600 and 35,000 [189-198]. (Mitochondrial DNA also codes for cytochrome b subunits.)... 

In order to define the translation site of the cytochrome b subunit(s) we proceeded as described for cytochrome oxidase (Table I) N. crassa was first labeled with [ C]leucine in the absence of inhibitors, and then with PHJleucine, either (1) in the absence of inhibitors, (2) in the presence of cycloheximide, (3) in the presence of chloramphenicol, or (4) during transitory presence of chloramphenicol. Purified cytochrome b was analyzed for and after gel filtration in bile acid-KCl solution and after gel electrophoresis in dodecylsulfate solution. It should be remembered that in the bile acid solution, the polypeptide and heme composition of cytochrome b remains intact, whereas in dodecylsulfate, the heme is dissociated from polypeptides. The results of these labeling experiments are shown in Table I and in Figs. 16 and 17. 

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