Heme-cytochrome

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"... 

The chain of carriers between the two photosystems includes the cytochrome b6f complex and a copper protein, plastocyanin. Like the mitochondrial and bacterial cytochrome be i complexes, the cytochrome b(J complex contains a cytochrome with two b-type hemes (cytochrome b6), an iron-sulfur protein, and a c-type cytochrome (cytochrome /). As electrons move through the complex from reduced plastoquinone to cytochrome/, plastoquinone probably executes a Q cycle similar to the cycle we presented for UQ in mitochondria and photosynthetic bacteria (see figs. 14.11 and 15.13). The cytochrome bbf complex provides electrons to plastocyanin, which transfers them to P700 in the reaction center of photosystem I. The electron carriers between P700 and NADP+ and between H20 and P680 are... 

E. McDonald, Biosynthesis of the pigments of life Formation of the macrocycle. Nature 285 17, 1980. This paper discusses the steps in tetrapyrrole biosynthesis and the pathways diverting this nucleus to chlorophylls, hemes, cytochromes, and other macrocyclic pigments. 

Fig. 8.12. NOESY (A) and ROESY (B) spectrum of a four heme cytochrome. The exchange cross peaks in the two spectra have the same sign and give information on different interactions [15].

The association of proton movement with electron transport is not reflected in the fatty acyl desaturase system universal to endomembranes. In these enzymes the dehydrogenase, NADH cyt b5 reductase and the cytochrome b5 (a single heme cytochrome) are associated exclusively with the cytosolic side of the membrane by acyl groups and have no transmembrane segment. The cytochrome b5 oxidase associated with the desaturation of fatty acyl CoA may be transmembranous but has not been associated with proton movement. It is an iron-containing protein. The other type of endomembrane cytochromes are the P-450 group of cytochrome bs... 

Echalier A, Goodhew CF, Pettigrew GW et al (2006) Activation and catalysis of the di-heme cytochrome c peroxidase from Paracoccus pantotrophus. Structure 14 107-117... 

Fiilop V, Ridout CJ, Greenwood C et al (1995) Crystal-structure of the di-heme cytochrome-c peroxidase from Pseudomonas aeruginosa. Structure 3 1225-1233... 

These ligands are especially important because many naturally occurring, metal-containing compounds such as chlorophylls, heme, cytochromes, etc., contain macrocycles. Some examples of these ligands are shown in Fig. 9-3. 

The structure of the reaction centre from Rps. viridis is similar to that of Rb. sphaeroides. The principal differences are that the Rps. viridis reaction centre contains BChl b and BPhe b in place of BChl a and BPhe a, menaquinone-9 in place of UQio at the Qa site, and the carotenoid hydroneurosporene in place of spheroidene/spheroidenone. The other major difference is the presence of a fourth extra-membrane subunit in the Rps. viridis reaction centre that consists of a tetra-heme cytochrome that is attached to the periplasmic faces of the L and M subunits (Deisenhofer et ah, 1995 Deisenhofer and Michel, 1989a,b Michel et ah, 1986 Deisenhofer et al., 1985 Deisenhofer et al., 1984). 

A number of derivatives of this complex have been prepared (see Multi-Heme Cytochromes Enzymes). Substitution of carbonyl ligands by other donors, such as that shown in equation (15), gives rise to a wide range of complexes. 

The Nine-heme Cytochrome cj. The nine-heme cytochrome C3 (9HCC3), originally reported to contain 12 hemes, was referred to as the dodecaheme cytochrome c. Only when its structure became available was the correct number of hemes established as nine. This cytochrome of 37.8kDa has been isolated from D. desulfuricans strains ATCC 27774... 

C554 is proposed to bind, and may thus be the electron exit heme. Cytochrome C554 also has two coplanar diheme pairs, which may indicate that it can also accept two electrons simultaneously. This cytochrome then transfers electrons to the membrane-bound tetraheme cytochrome Cm552 (see Section 4), which is a good candidate to reduce the membrane ubiquinone pool, from where electrons are partitioned between the ammonia monooxygenase reaction, the aerobic respiratory chain, and reverse electron transport. ... 

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