Bacterial Cytochromes

Many key protein ET processes have become accessible to theoretical analysis recently because of high-resolution x-ray stmctural data. These proteins include the bacterial photosynthetic reaction centre [18], nitrogenase (responsible for nitrogen fixation), and cytochrome c oxidase (the tenninal ET protein in mammals) [19, 20]. Although much is understood about ET in these molecular machines, considerable debate persists about details of the molecular transfonnations. 

Many enzymes have been the subject of protein engineering studies, including several that are important in medicine and industry, eg, lysozyme, trypsin, and cytochrome P450. SubtiHsin, a bacterial serine protease used in detergents, foods, and the manufacture of leather goods, has been particularly well studied (68). This emphasis is in part owing to the wealth of stmctural and mechanistic information that is available for this enzyme. 

FIGURE 22.17 The R. viridis reaction center is coupled to the cytochrome h/Cl complex through the quinone pool (Q). Quinone molecules are photore-duced at the reaction center Qb site (2 e [2 hv] per Q reduced) and then diffuse to the cytochrome h/ci complex, where they are reoxidized. Note that e flow from cytochrome h/ci back to the reaction center occurs via the periplasmic protein cytochrome co- Note also that 3 to 4 are translocated into the periplasmic space for each Q molecule oxidized at cytochrome h/ci. The resultant proton-motive force drives ATP synthesis by the bacterial FiFo ATP synthase. (Adapted from Deisenhofer, and Michel, H., 1989. The photosynthetic reaction center from the purple bac-terinm Rhod.opseud.omoaas viridis. Science 245 1463.)... 

Cytochrome enzymes, 2, 772 Cytochrome a3 oxidase, 6, 697 Cytochrome c oxidase, 6, 683 copper complexes, 2,724,772 Cytochrome oxidases, 6, 624 bacterial, 6,696... 

Cytochromes and Iron Sulfur Proteins in Bacterial Sulfur Metabolism (U. 

The use of direct electrochemical methods (cyclic voltammetry Pig. 17) has enabled us to measure the thermodynamic parameters of isolated water-soluble fragments of the Rieske proteins of various bci complexes (Table XII)). (55, 92). The values determined for the standard reaction entropy, AS°, for both the mitochondrial and the bacterial Rieske fragments are similar to values obtained for water-soluble cytochromes they are more negative than values measured for other electron transfer proteins (93). Large negative values of AS° have been correlated with a less exposed metal site (93). However, this is opposite to what is observed in Rieske proteins, since the cluster appears to be less exposed in Rieske-type ferredoxins that show less negative values of AS° (see Section V,B). 

FIGURE 3.1 Bacterial oxygenation systems (excluding cytochrome P450 systems). (From Neilson, A.H. and Allard, A.-S. Microbial metabolism of PAHs and heteroarenes, The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, 1998. With permission.)... 

Unusual aspects of bacterial cytochrome P450 systems are worth pointing out ... 

Karlson U, DF Dwyer, SW Hooper, ERB Moore, KN Timmis, LD Eltis (1993) Two independently regulated cytochromes P-450 in a Rhodococcus rhodochrous strain that degrades 2-ethoxyphenol and 4-methoxybenzoate. J Bacterial 175 1467-1474. 

Koga H, H Aramaki, E Yamaguchi, K Takeuchi, T Horiuchi, 1C Gunsdalus (1986) camR, a negative regulator locus of the cytochrome P-450 jjj hydroxylase operon. J Bacterial 166 1089-1095. 

Nagy 1, G Schools, F Compermolle, P Proost, J Vanderleyden, R De Mot (1995b) Degradation of the thiocar-bamate herbicide EPTC S-ethyl dipropylcarbamoylthioate and biosafening by Rhodococcus sp. strain N186/21 involve an inducible cytochrome P-450 system and aldehyde dehydrogenase. J Bacterial 177 676-687. 

Smith DJ, VJJ Martin, WH Mohn (2004) A cytochrome P450 involved in the metabolism of abietane diterpenoids by Pseudomonas abietaniphila BMKE-9. J Bacterial 186 3631-3639. 

Seeliger S, R Cord-Ruwisch, B Schink (1998) A periplasmic and extracellular c-type cytochrome of Geobacter sulfurreducens acts as a ferric iron reductase and as an electron carried to other acceptors or to partner bacteria. J Bacterial 180 3686-3691. 

Omer CA, R Lenstra, PJ Little, C Dean, JM Tepperman, KJ Leto, JA Romesser, DP O Keefe (1990) Genes for two herbicide-inducible cytochromes P-450 from Streptomyces griseolus. J Bacterial 172 3335-3345. 

Abramson J, Svensson-Ek M, Byrne B, Iwata S. 2001. Structure of cytochrome c oxidase A comparison of the bacterial and mitochondrial enzymes. Biochim Biophys Acta 1544 1. 

Pitcher RS, Watmough NJ. 2004. The bacterial cytochrome ebbs oxidases. Biochim Biophys Acta 1655 388. 

Fang and Burris (63) isolated a c-type cytochrome from the cells of Hydrogenomonas eutropha. Type c cytochromes have been isolated from the cells of a number of other bacterial species (64) and a three dimensional model has been proposed for the cytochrome C551 of Pseudomonas aeru-... 

Otey, C.R., Bandara, G., Lalonde, J.L. et al. (2006) Preparation of human metabolites of propranolol using laboratory-evolved bacterial cytochromes P450. Biotechnology and Bioengineering, 93, 494 499. 

The flow of electrons occurs in a similar manner from the excited pigment to cytochromes, quinones, pheophytins, ferridoxins, etc. The ATP synthase in the mitochondria of a bacterial system resembles that of the chloroplast—chloroplast proton translocating ATP synthase [37]. 

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