Oxygen cytochromes

Dawson, J. H., et al. (1986) Oxygenated cytochrome P450cam and chloroperoxidase direct evidence for sulfur donor ligation trans todioxygen and structural characterization using EXAFS spectroscopy. J. Am. Chem. Soc. 108, 8114-8116. 

Dolin, M. I. 1955. The DPNH-oxidizing enzymes of Streptococcus faecalis. II. The enzymes utilizing oxygen, cytochrome c, peroxide and 2,6-ichlorophenol or ferricya-nide as oxidants. Arch. Biochem. Biophys. 55, 415-435. 

The active oxygen -cytochrome P450 complex is a powerful oxidizing agent towards almost any organic compound, including alkanes, and the central iron-porphyrin complex has been depicted as... 

It was shown by Strength et al. (261) that the oxidation of choline by a particulate preparation from rat liver was considerably enhanced upon addition of NAD. Others showed that choline oxidation by isolated rat liver mitochondria was completely inhibited by Amytal when oxygen, cytochrome c, ferricyanide, or methylene blue was the electron acceptor -264) Choline dehydrogenase activity of particles and soluble prepa-... 

In the absence of oxygen cytochrome c rapidly (ti/s 10 msec) reduced oxidase (IV) to oxidase (II), but subsequent changes are slow even in the presence of excess cytochrome c- and do not involve additional electrons 66, 107, 153, 192-194). The initial rapid reduction which was followed spectrophotometrically in the visible region by the disappearance of cytochrome c"- or in the EPR by the disappearance of the gr — 2 (copper) and gf 3 (low-spin iron) signals 66, 194) was found to be independent of the presence of cyanide in the reaction mixture 192). These observations have been interpreted in terms of the initial reduction of oxi-... 

Figure 4-2 a Simplified depiction of the nicposed activated oxygen-cytochrome P-tSd-subitrate complex. Note the simplified opoproiem portion and the heme (protoporphyrin IX) portion or cytochrome P-450 and the close proximity of the substrate R-H undergoing oxidation... 

Orii Y, Webster DA (1986) Photodissociation of oxygenated cytochrome o (s) (Vitreoscilla) and kinetic studies of reassociation. J Biol Chem 261 3544-3547 Oro J (1994) Early chemical stages in the origin of life. In Bengtson S (ed) Early life on Earth. 

It is noteworthy that the 0-0 stretching Raman band of oxygenated cytochrome P-450 was identified at 1140 cm (1074 cm for 02) by using a spinning cell at... 

By using an anti-cytochrome antibody it was established that cytochrome bs also was required for the desaturase which introduces a double bond at position 6 in a fatty acid (Okayasu et a/., 1977 Lee et a/., 1977). Recently a 6-desaturase has been purified from rat liver and shown to be a single polypeptide of 66,000 daltons containing one atom of nonheme iron. NADH, molecular oxygen, cytochrome 65, cytochrome 65 reductase and lipid or detergent were all required in order for linoleoyl-CoA to be desatu-rated (Okayasu et a/., 1981). 

Fig. 16. EXAFS spectra of oxygenated cytochrome P-450 at pH 7.4 (top) and oxygenated chloroperoxidase at pH 6.0 (bottom) obtained at — 80°C. A mixed solvent was employed consisting of ethylene glycol (65% v/v) and 0.035 M potassium phosphate buffer (plus 4mM camphor for P-450-CAM). Spectra have been multiplied by to enhance the visibility of oscillations at high k. Reproduced with permission from Ref. [116]...

Lipscomb JD, Sligar SG, Namtvedt MJ, Gunsalus 1C (1976) Autooxidation and hydroxylation reactions of oxygenated cytochrome P-450cam. J Biol Chem 251 1116-1124... 

Baron J, Hildebrand AG, Peterson JA, Estabrook RW (1973) The role of oxygenated cytochrome P-450 and of cytochrome b5 in hepatic microsomal drug oxidations. Drug Metab Dispos 1 129-138... 

Ishimura Y, Ullrich V, Peterson JA (1971) Oxygenated cytochrome P-450 and its possible role in enzymic hydroxylation. Biochem Biophys Res Commun 42 140-146... 

Of the a and b cytochromes little is known save that the haem of cyto-chrome-a is similar to that in chlorocruorin and that the haem of cytochrome-6 is protohaem. Cytochrome-a is not autoxidizable (modification, of the valency of the iron by the action of molecular oxygen) whilst cytochrome-6 is. It has been possible to identify three new haemochromogens whose spectra are similar to the spectrum of c3rtochrome -a these are cyto-chromes-fli, -a and -a. C3rtochromes-ai and -a replace cytochrome-a in certain bacteria where this latter substance is missing. Cytochrome-Cs is identical with cytochrome-oxidase, otherwise known as Warburg s respiratory enzyme. In the ferrous state it is autoxidizable, that is, it is oxidized to the ferric state by molecular oxygen. Cytochrome-a, which is not autoxidizable, is oxidized by cytochrome-aj (cytochrome-oxidase). 

The cytochrome P-450 pathway enzymes (not shown on Figure 2) are monooxygenases, whereas COX is a dioxygenase (Estabrook et al, 1982). Unlike COX and lipoxygenases, cytochrome P-450 enzymes require several cofactors to metabolize fatty acids, including P-450 reductase and NADPH (Fitzpatrick and Murphy, 1989). In the presence of these cofactors and molecular oxygen, cytochrome P-450 can serve as the catalyst for the biotransformation of EPA to a variety of oxygenated metabolites (Fitzpatrick and Murphy, 1989). These include epoxides and hydroxy fatty acids such as epoxy-EPA (EEP) and HEPE (Kiss et al, 1998). 

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