Cytochrome directional

Jushchyshyn MI, Hutzler JM, Schrag ML, Wien-kers LC (2005) Catalytic turnover of pyrene by CYP3A4 evidence that cytochrome directly induces positive cooperativity. Arch Biochem Biophys 438 21-28... 

Dyer R B, Einarsdottir 6, Killough P M, Lopez-Garriga J J and Woodruff W H 1989 Transient binding of photodissociated CO to of eukaryotic cytochrome oxidase at ambient temperature. Direct evidence from time-resolved infrared spectroscopy J. Am. Chem. Soc. Ill 7657-9... 

Complex rV is called, cytochrome c oxidase because it accepts electrons from cytochrome c and directs them to the four-electron reduction of O2 to form H2O ... 

Oae and coworkers oxidized several diaryl, dialkyl and alkyl aryl sulfides to their corresponding sulfoxides using purified cytochrome P-450 obtained from rabbit liver microsomes138. In agreement with expectations, this enzyme did not exhibit much stereospecificity. Some examples including the observed e.e. values are shown by 121-125. A model was proposed to account for the absolute configurations of the sulfoxides produced (126). The sulfur atom is preferentially oxidized from the direction indicated. 

When the second-site revertants were segregated from the original mutations, the bci complexes carrying a single mutation in the linker region of the Rieske protein had steady-state activities of 70-100% of wild-type levels and cytochrome b reduction rates that were approximately half that of the wild type. In all these mutants, the redox potential of the Rieske cluster was increased by about 70 mV compared to the wild type (51). Since the mutations are in residues that are in the flexible linker, at least 27 A away from the cluster, it is extremely unlikely that any of the mutations would have a direct effect on the redox potential of the cluster that would be observed in the water-soluble fragments. However, the mutations in the flexible linker will affect the mobility of the Rieske protein. Therefore, the effect of the mutations described is due to the interaction between the positional state of the Rieske protein and its electrochemical properties (i.e., the redox potential of the cluster). 

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). 

Rosenberg, D.W. and Drummond, G.S. (1983). Direct in vitro effects of TBTO on hepatic cytochrome P450. Biochemical Pharmacology 32, 3823-3829. 

Szklarz GD, Halpert JR. Use of homology modeling in conjunction with site-directed mutagenesis for analysis of structure-function relationships of mammalian cytochromes P450. Life Sci 1997 61 2507-20. 

Cytochrome PTSOiy, carries out comparable reactions for removal of the side chain of pregnenolone, and two reactions have been described both of which involved loss of acetate—17a-hydroxylation and formation of the 17-keto compound, and direct formation of the A -ene (Figure 3.19c) (Akhtar et al. 1994). 

Attention has been directed to the reactions catalyzed by cytochrome P450s that bring about important reactions leading to the loss of angular methyl groups at C-10 (with concomitant aromatiza-tion of ring A) and C-14, and the C-17 -COCHj side chain. These reactions are discussed further in Chapter 3, Part 1. The transformations of steroids and their precursor lanosterol have been extensively... 

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