Catalytic cycles for cytochrome

Figure 17-E-8 A schematic catalytic cycle for cytochrome P-450. The porphyrin group is not shown except in the view at the top. An asterisk indicates a proposed intermediate.

Scheme 10.4 The catalytic cycle of cytochrome P450. Only one possible valence structure of the oxoferrous species IV has been depicted for clarity. See text for details.

The answers are 34-g, 35-a, 36-d. (Katzung, pp 53—56J There are four major components to the mixed-function oxidase system (1) cytochrome P450, (2) NAD PH, or reduced nicotinamide adenine dinucleotide phosphate, (3) NAD PH—cytochrome P450 reductase, and (4) molecular oxygen. The figure that follows shows the catalytic cycle for the reactions dependent upon cytochrome P450. 

Figure 9.4. Generalized cytochrome P450 catalytic cycle for the oxidation of substrates (Adapted from Guengerich, F. P., Common and uncommon cytochrome P450 reactions related to metabolism and chemical toxicity. Chem. Res. Toxicol. 14, 611-650, 2001.)...

One motivation for the characterization of the above compounds has been to more fully understand the involvement of such higher valent manganese porphyrin complexes in model systems which imitate the catalytic activity of monooxygenase cytochrome P-450 and related enzymes. The catalytic cycle of cytochrome P-450 appears to involve the binding and reduction of molecular oxygen at a haem centre followed by the ultimate formation of a reactive iron oxo complex which is responsible for oxidation of the substrate. For example, cytochrome P-450 is able to catalyse alkane hydroxylation with great selectivity. 

Scheme 8 A catalytic cycle for oxygen activation and transfer by cytochrome P450 (S = substrate, e.g. alkene X = e.g.

The key features of the presently accepted catalytic cycle for a cytochrome P450 enzyme are summarized in Fig. 17-E-8. The multistep process includes four stable... 

Figure 8.2 Generalized scheme showing the catalytic cycle of cytochrome P450 enzymes in monooxygenation reactions. Fe = iron atom in P450 heme. RH = substrate. ROH = product. b5 = cytochrome bs. ox and red indicate the reduced and (1 electron) oxidized states of the reductase involved in the electron transfer. See text for details. (From Guengerich, F.P., Client. Res. Toxicol. 14, 611, 2001. With permission.)...

FIGURE 3. The Catalytic Cycle for Flavocytochrome 62 F, flavin H, heme Cyt c, cytochrome c. Electrons are shown as hlack dots and are used to indicate the two-electron reduced flavin (hydroquinone), F with two dots one-electron reduced flavin (semiquinone), F with one dot reduced heme, H with one dot reduced cytochrome c, Cyt c with one dot. The rate constants shown are for S. cerevisiae flavocytochrome hi at 25 C, pH 7.5, I = O.IOM. The whole catalytic cycle turns over at approximately 100 s ". The details of the cycle are described in the main text. 

Oxoiron(IV) tefraphenylchlorin complexes have been prepared as the first models of a reaction intermediate in the catalytic cycle of cytochrome d Optical absorption spectra show a characteristic red-shified band at 630 nm as observed in the oxoferryl intermediate of cytochrome d, and the proton NMR spectra of the N-Melm complex exhibit very small hyperfine shifts of the pyrrole protons, as is true for oxoferryl porphyrin complexes. The pyrroline protons of the saturated pyrrole ring show unusual splitting into upheld and downfield resonances. The N-Melm complex also shows normal Fe =0 stretching frequencies as compared to the corresponding oxoferryl porphyrin complexes. And finally, for iron porphycenes, both peroxo and ferryl intermediates have been detected by H NMR spectroscopy during the oxygenation of the Fe complexes. ... 

Figure 4. Catalytic cycle of cytochrome P450 including the postulated structures of the putative intermediates. RH represents the substrate and R(0)H represents the product. The porphyrin macrocycle is abbreviated as a parallelogram with nitrogens at the comers. See text for details. (Adapted from Ref. [6].)...

Figure 7 Possible catalytic cycle for O2 reduction in cytochrome oxidase.

Figure 30. Natural catalytic cycle for the hydroxylation of organic compounds catalyzed by the Cytochrome (Cyt) P-450cam monooxygenase system (Cyp = Cyt. P-450 hemeprotein Pdx = putidaredoxin).

FIGURE 13.12 Catalytic cycle of cytochrome P450. The cytochrome P450 catalytic cycle with the compound 1-Uke ferryl species highlighted by a blue square. The haem is represented by the iron between two bars, which stand for the porphyrin framework. RH is a hydrocarbon substrate and ROH its alcohol product. (From Johnston et al, 2011. Copyright 2011, with permission from Elsevier.)... 

Ogliaro, F., S.P. de Visser, S. Cohen, P.K. Sharma, and S. Shaik (2002). Searching for the second oxidant in the catalytic cycle of cytochrome P450 A theoretical investigation of the iron(lll)- hydroper-0X0 species and its epoxidation pathways. J. Am. Chem. Soc. 124, 2806-2817. 

Figure 6.1. The general catalytic cycle of cytochrome P450 enzymes. The [Fe ] stands for the resting ferric state of P450, and SH for a substrate molecule. The shunt pathway utilizing HjOj is shown as are three sites for the...

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