b‐Type Cytochrome Electron Carriers: Cytochromesb₅₆₂andb₅, and Flavocytochromeb₂

Abstract

b‐Type cytochromes form a class of proteins that contain a heme (iron‐protoporphorin IX) bound non‐covalently to its polypeptide chain with two of its side chains coordinated to the iron. One of these side chains is always histidine and the other can be histidine or methionine. Cytochromes b 5 and b 562 are simple mono‐domain proteins that contain heme as the only prosthetic group and histidine and methionine, respectively, as the second heme ligand. Flavocytochrome b 2 also contains histidine as the second heme ligand, but contains a second prosthetic group, flavin mononucleotide (FMN), that resides in a separate domain. Cytochromes b 5 and b 562 each mediate intracellular electron transfer between redox partners, the former within the endoplasmic reticulum of mammalian cells and the latter within bacteria. Flavocytochrome b 2 catalyzes the oxidation of lactic acid within yeast mitochondria, with the cytochrome domain mediating electron transfer from substrate‐reduced FMN to exogenous cytochrome c. The structural, electrochemical, and catalytic properties of these three proteins are presented, along with the results of mutagenesis.

The Transcription Regulator RcoM-2 from Burkholderia xenovorans Is a Cysteine-Ligated Hemoprotein That Undergoes a Redox-Mediated Ligand Switch

“…The RrCooA homodimer consists of two domains: an N-terminal heme-binding regulatory domain and a C-terminal helix-turn-helix DNA-binding domain (20). The RrCooA dimer binds two b-type heme cofactors in the regulatory domain; the Fe(III) heme iron is coordinated by cysteine(thiolate) (Cys 75 ) and by the nitrogen of the opposing monomer's N-terminal proline (Pro 2 ) (21). When the heme is reduced, the cysteine(thiolate) is replaced with a neighboring histidine (His 77 ) (22,23), which poises the protein to bind CO via replacement of the coordinated proline.…”

Fruit Juices as A Source of Infection. A Review

“…The risk is more when there is an outbreak of infection. Outbreaks of sickness brought about by microscopic organisms and parasites have been connected to juices for a long time (Mathews and Scott Mathews, 2006).Although the affirmation of the causative agents in these outbreaks has been abnormal. The causticity of organic product juice has been truly thought to be an important deterrent against endurance and development of foodborne pathogens(Tribst, de Souza Sant'Ana and de Massaguer, 2009).…”