Cytochrome types

The large number of cytochromes identified contain a variety of porphyrin ring systems. The classification of the cytochromes is complicated because they differ from one organism to the next the redox potential of a given cytochrome is tailored to the specific needs of the electron transfer sequences of the particular system. The cytochromes are one-electron carriers and the electron flow passes from one cytochrome type to another. The terminal member of the chain, cytochrome c oxidase, has the property of reacting directly with oxygen such that, on electron capture, water is formed ... 

The CYPs, the carbon monoxide-binding pigments of microsomes, are heme proteins of the b cytochrome type. Originally described as a single protein, there are now known to be more than 2000 CYPs widely distributed throughout animals, plants, and microorganisms. A system of nomenclature utilizing the prefix CYP has been devised... 

Fig. 19.2 The heme group Type A hemes are found in cytochrome Type B hemes are found in hemoglobin, myoglobin, peroxidase, and cytochrome ft Type C heme.s are found in cytochrome c chloroheme is found in chlorocruorin.

Redox proteins that include quinone cofactor units play important roles in biological ET processes. Some of the quinoproteins include the quinone cofactor in a non-covalently linked configuration, such as the pyrroloquinoline quinone, PQQ, dependent enzymes, whereas other quinoproteins include the quinone cofactor covalently-linked to the protein, for example topaquinone (2,4,6-trihydroxyphenylalanine quinone, TPQ) dependent enzymes. A number of quinoproteins include in addition to the quinone cofactor an ET cofactor unit in another protein subunit. These cofactors may be metal ions or a cytochrome-type heme cofactor such as D-fructose dehydrogenase that is a heme containing PQQ-dependent enzyme. ... 

The formation of methane by the methanogens is called carbon dioxide respiration, as described previously (p. 112). In general, cytochromes occur as the electron carrier in the respiration. Thus, some methanogens have cytochromes b and c. However, not all methanogens have cytochromes, as already mentioned. This may mean that carbon dioxide respiration is an early evolving stage of the respiration from the noncytochrome-type to the cytochrome-type. The electron transfer systems of the sulfur respirers contain cytochrome b or cytochromes b and c (Hedderich et al., 1999). In the iron respiration system of Pyrobaculum islandicum, cytochrome b seems to participate in the Fe(III) reducing system (Childers and Lovley, 2001). These results will show that the fundamental features of the respiration may have already been established in the hyperthermophilic chemolithoautotrophic archaea (Fig. 7.2). 

The TypeIITetraheme Cytochrome. Type II cytochromes C3 (4HCc3TpII) are a second group of tetraheme cytochromes C3 that have structural, genetic, and reactivity features that distinguish them from the previously characterized dHCcsTpIs. D. africanus was the first Desulfovibrio sp. reported to contain a 4HCc3TpII, and was referred to as acidic cytochrome A homolog of this cytochrome... 

All these intermediates except for cytochrome c are membrane-associated (either in the mitochondrial inner membrane of eukaryotes or in the plasma membrane of prokaryotes). All three types of proteins involved in this chain— flavoproteins, cytochromes, and iron-sulfur proteins—possess electron-transferring prosthetic groups. 

Fig. 11a. Fractionation of (/) chymotrypsinogen A, (2) cytochrome C and (3) lysozyme on strong cation exchangers, a) Support Fractogel TSK 650(s)SP (conventional type) sample, 1 mg each flow rate, 1 ml/min column size, 150 x 10 mm T.D. Solvent A = 0.02 mol/1 phosphate, pH 6.0 solvent B = A + 1 mol/1 NaCl gradient, 0-10 min, 0% B 10-70 min, 0-100% B. b) Support Fractogel EMD 650(s)SO( — (tentacle type) conditions as in (a) [78]...

Complex III 280 kDa 11 28 type hemes (b and bg) bound to same mitochondrially coded peptide 1 C heme (cytochrome c,) 1 Fe-S center Rieske factor Spans membrane, cytochrome b, and b in membrane, cytochrome c, and Fe-S center on outer face 0.25-0.53 Pumps protons out of matrix during electron transport/2e"... 

Cytochrome c 12.3 kDa 1 C type heme Inter membrane space, loosely associated with inner membrane 0.8-1.02 ... 

Complex IV 200 kDa (probably as a dimer) 13 2 A type hemes (a, aj) 2 or 3 Cu Spans inner membrane, cytochrome c site on outer face 0.16-1.00 Pumps protons out of matrix during electron transport/4e"... 

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