Cytochrome distribution

At least 12 genes are involved in the formation of nitrate reductase in various Enterobacteriaceae, 5 nar genes have been identified in Pseudomonas aeruginosa and 13 Chi mutations have been characterized in Bacillus licheniformis (Stouthamer, 1976). The physiological properties of chlorate-resistant mutants have been characterized and their location on the circular chromosome determined. Chi mutations have a pleotropic affect such characteristics as dehydrogenase activity, cytochrome distribution, and membrane protein composition may be influenced. The different Cfi/ mutants are able to synthesize various components of the complex nitrate reductase molecule. It is possible, in some instances, to form active enzyme by mixing components extracted from the appropriate mutants (Stouthamer, 1976). 

Plasma levels of 3—5 p.g/mL are obtained two hours after adraiinistration of 200 mg ketoconazole. No accumulation in the bloodstream was noted after a 30-wk treatment with this dose. The half-life is approximately eight hours. When ketoconazole is taken with meals, higher plasma levels are obtained. Distribution studies using radioactive ketoconazole in rats show radioactivity mainly in the Hver and the connective tissue. Radioactivity is also present in the subcutaneous tissue and the sebaceous glands. After one dose of 200 mg in humans, ketoconazole is found in urine, saUva, sebum, and cenimen. Like miconazole, the mode of action is based on inhibition of the cytochrome P-450 dependent biosynthesis of ergosterol. This results in disturbed membrane permeabiUty and membrane-bound enzymes (8,10,23,25). 

Both attractive forces and repulsive forces are included in van der Waals interactions. The attractive forces are due primarily to instantaneous dipole-induced dipole interactions that arise because of fluctuations in the electron charge distributions of adjacent nonbonded atoms. Individual van der Waals interactions are weak ones (with stabilization energies of 4.0 to 1.2 kj/mol), but many such interactions occur in a typical protein, and, by sheer force of numbers, they can represent a significant contribution to the stability of a protein. Peter Privalov and George Makhatadze have shown that, for pancreatic ribonuclease A, hen egg white lysozyme, horse heart cytochrome c, and sperm whale myoglobin, van der Waals interactions between tightly packed groups in the interior of the protein are a major contribution to protein stability. 

For many solubilized enzymes the greatest catalytic activity and/or changes in conformation are found at R < 12, namely, when the competition for the water in the system between surfactant head groups and biopolymers is strong. This emphasizes the importance of the hydration water surrounding the biopolymer on its reactivity and conformation [13], It has been reported that enzymes incorporated in the aqueous polar core of the reversed micelles are protected against denaturation and that the distribution of some proteins, such as chymotrypsine, ribonuclease, and cytochrome c, is well described by a Poisson distribution. The protein state and reactivity were found markedly different from those observed in bulk aqueous solution [178,179],... 

They are widely distributed across species. Bacteria possess cytochrome P450s, and P450cani (involved in the metabolism of camphor) of Pseudomonas putida is the only P450 isoform whose crystal stmcture has been established. 

The cytochrome P-450-dependent metabolism of trichloroethylene was studied in hepatic microsomal fractions from 23 different humans (Lipscomb et al. 1997). CYP2E1 was the predominant form of P-450 responsible for the metabolism of trichloroethylene in humans. Incubations of trichloroethylene with the microsomal preparations resulted in hyperbolic plots consistent with Michaelis-Menton kinetics. The values ranged from 12 to 55.7 pM, and were not normally distributed, and the values range from 490 to 3,455 pmol/min/mg protein and were normally distributed. The study authors concluded that the human variability in metabolism of trichloroethylene via P-450-dependent pathways was within a 10-fold range. 

Cytochrome P450-type monooxygenase systems, which have a generally low substrate specificity, are widely distributed in the species of fish used for toxicity testing (Funari et al. 1987). 

The reductase in Geobacter sulfurreducens is located in the outer membrane and a soluble Fe(III) reductase has been characterized from cells grown anaerobically with acetate as electron donor and Fe(III) citrate or fumarate as electron acceptor (Kaufmann and Lovley 2001). The enzyme contained Fe, acid-labile S, and FAD. An extracellular c-type cytochrome is distributed in the membranes, the periplasm, and the medium, and functions as a reductase for electron transfer to insoluble iron hydroxides, sulfur, or manganese dioxide (Seeliger et al. 1998). 

Wu, M. L., Wu, X. H. Chen, S. C. (2005). Study on tissue distribution difference of cytochrome P450 2C19 in Chinese population Han. Journal of Chinese Pharmaceuticals, 40(3), 215-18. 

Wacher, V. J., Wu, C. Y., Benet, L. Z., Overlapping substrate specificities and tissue distribution of cytochrome P450 3A and P-glycoprotein implications for drug delivery and activity in cancer chemotherapy, Mol. Carcinogen. 1995, 13, 129-134. 

The CNS contains much smaller amounts of drug-metabolizing enzymes than does the liver. The concentrations of the main enzymes in the brain, members of the cytochrome P450 (CYP) superfamily, are only 0.25% of concentration in the liver. But the brain enzymes are not uniformly distributed, as they are in the liver they are concentrated in specific brain areas. Theoretical models have explained that drug metabolism in the CNS cannot influence drug distribution in the blood, but there are marked differences in brain tissue levels depending on the presence... 

In the practice of solid-state bioEPR, a Lorentzian line shape will be observed at relatively high temperatures and its width as a function of temperature can be used to deduce relaxation rates, while a Gaussian line will be observed at relatively low temperatures and its linewidth contains information on the distributed nature of the system. What exactly is high and low temperature, of course, depends on the system for the example of low-spin cytochrome a in Figure 4.2, a Lorentzian line will be observed at T = 80°C, and a Gaussian line will be found at T 20°C, while at T 50°C a mixture (a convolution) of the two distributions will be detected. 

Formally, this procedure is correct only for spectra that are linear in the frequency, that is, spectra whose line positions are caused by the Zeeman interaction only, and whose linewidths are caused by a distribution in the Zeeman interaction (in g-values) only. Such spectra do exist low-spin heme spectra (e.g., cytochrome c cf. Figure 5.4F) fall in this category. But there are many more spectra that also carry contributions from field-independent interactions such as hyperfine splittings. Our frequency-renormalization procedure will still be applicable, as long as two spectra do not differ too much in frequency. In practice, this means that they should at least be taken at frequencies in the same band. For a counter-example, in Figure 5.6 we plotted the X-band and Q-band spectra of cobalamin (dominated by hyperfine interactions) normalized to a single frequency. To construct difference spectra from these two arrays obviously will generate nonsensical results. 

T.J. Kemp, Warwick Is it not the case that the product distribution in hydroxylation of organic molecules by Fenton s reagent differs in considerable detail from that realised by cytochrome P-450 ... 

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