Substrate specificity, of cytochrome

DeVoss JJ, Sibbesen O, Zhang ZP, et al. Substrate docking algorithms and prediction of the substrate specificity of cytochrome P450(cam) and its L244A mutant. J Am Chem Soc 1997 119 5489-5498. 

Iffland A, Gendreizig S, Tafemeyer P, Johnsson K (2001) Changing the substrate specificity of cytochrome c peroxidase using directed evolution. Biochem Biophys Res Commun 286 126-132... 

Taton, M. and Rahier, A. (1991) Properties and structural requirements for substrate specificity of cytochrome P450-dependent obtusifoliol 14 a-demethylase from maize Zea mays) seedlings. Biochem.., TUI, 483-92. 

Zhang Y, Guo X, Lin ET, Benet LZ. Overlapping substrate specificities of cytochrome P450 3A and P-glycoprotein for a novel cysteine protease inhibitor. Drug Metab Dispos 1998 26(4) 360-366. 

Wu ZL, Podust LM, Guengerich FP (2005) Expansion of substrate specificity of cytochrome P450 2A6 by random and site-directed mutagenesis. J Biol Chem 280 41090 1100... 

Axarli I, Prigipaki A, Labrou NE (2005) Engineering the substrate specificity of cytochrome P450 CYP102A2 by directed evolution production of an efficient enzyme for bioconversion of fine chemicals. Biomol Eng 22 81-88... 

Mast, N., Norcross, R., Andersson, U. et al. Broad substrate specificity of human cytochrome P450 46A1 which initiates cholesterol degradation in the brain. Biochemistry 42 14284-14292, 2003. 

ANDERSEN, M.D., M0LLER, B.L., Cytochromes P450 from Cassava (Manihot esculenta Crantz) catalyzing the first steps in the biosynthesis of the cyanogenic glucosides linamarin and lotaustralin cloning, functional expression in Pichia pastoris and substrate specificity of the isolated recombinant enzymes, J. Biol. Chem., 2000,275, 1966-1975. 

De Rienzo, F., Fanelli, F., Menziani, M.C. and De Benedetti, P.G. (2000) Theoretical investigation of substrate specificity for cytochromes P450 IA2, P450 IID6 and P450 II IA4. Journal of Computer-Aided Molecular Design, 14, 93-116. 

The marine environment acts as a sink for a large proportion of polyaromatic hydrocarbons (PAH) and these compounds have become a major area of interest in aquatic toxicology. Mixed function oxidases (MFO) are a class of microsomal enzymes involved in oxidative transformation, the primary biochemical process in hydrocarbon detoxification as well as mutagen-carcinogen activation (1,2). The reactions carried out by these enzymes are mediated by multiple forms of cytochrome P-450 which controls the substrate specificity of the system (3). One class of MFO, the aromatic hydrocarbon hydroxylases (AHH), has received considerable attention in relation to their role in hydrocarbon hydroxylation. AHH are found in various species of fish (4) and although limited data is available it appears that these enzymes may be present in a variety of aquatic animals (5,6,7,8). 

Wolff, T., Distlerath, L. M., Worthington, M. T., et al. (1985) Substrate specificity of human liver cytochrome P-450 debrisoquine 4-hydroxylase probed using immunochemical inhibition and chemical modeling. Cancer Res. 45, 2116-2122. 

One important finding from purification studies as well as cloning and expressing of individual isoforms is that the lack of substrate specificity of microsomes for monooxygenase activity is not an artifact caused by the presence of several specific cytochromes. Rather, it appears that many of the cytochromes isolated are still relatively nonspecific. The relative activity toward different substrates does nevertheless vary greatly from one CYP isoform to another even when both are relatively nonspecific. This lack of specificity is illustrated in Table 7.2, using human isoforms as examples. 

Cytochrome P-450 found in bacteria and lever microsomes is a kind of hemoprotein that activates molecular oxygen to catalyze the hydroxylation of organic compounds in drug metabolism. For example, camphor is incorporated into cytochrome P-450 (forming P-450 cam) and then oxygenated to form 5-exo-hydroxycamphor as shown in Reaction 8 (25). The substrate specificity of this enzyme is not strict. How-... 

Lentz, O., Urlacher, V., and Schmid, R. D. 2004 Substrate specificity of native and mutated cytochrome P450 (CYP102A3) from Bacillus subtilis. J. Biotechnol., 108, 41-A9. 

As with the mixed-function oxidases involved in xenobiotic metabolism, the substrate specificity of the steroid hydroxylases is dictated, in part, by the existence of multiple forms of both microsomal and mitochondrial cytochrome P-450s and further opportunities for specificity are provided by the distinct localization of the various enzymes in either the mitochondria or the endoplasmic reticulum. 

The formation of the methylenedioxy bridge in Berberis has been found to be caused by the demethylating activity of a peroxidase (POD) found within the vesicle. It was also found that the cytochrome P450-requiring enzyme (canadine synthase) from microsomes of Berberis, Thalictrum and Coptis species formed the methylene bridge in (S)-tetrahydrocolumbamine (Ikezawa et al, 2003), but not in the quaternary alkaloid columbamine (Galneder et al, 1988 Zenk, 1995). Because of the substrate specificity of canadine s)mthase, the berberine pathway is considered to be that presented in Fig. 2.5 (Rueffer and Zenk, 1994). Columbamine, once proposed as an alternative route to berberine, is however converted to palmatine by a specific methyltransferase first isolated from Berberis wilsoniae cell cultures (Rueffer and Zenk, 1985 Ikezawa et al, 2003). 

Terfloth L, Bienfait B, Gasteiger J. Ligand-based models for the isoform specificity of cytochrome P450 3A4, 2D6, and 2C9 substrates. J. Chem. Inf. Model. 2007 47 1688-1701. 

The understanding of the degradation of natural products such as camphor has been greatly enhanced by understanding the catalytic cycle of the cytochrome P-450 enzyme P-450cam in structural detail.3,4 These enzymes catalyze the addition of 02 to nonactivated hydrocarbons at room temperatures and pressures - a reaction that requires high temperature to proceed in the absence of a catalyst. O-Methyltransferases are central to the secondary metabolic pathway of phenylpropanoid biosynthesis. The structural basis of the diverse substrate specificities of such enzymes has been studied by solving the crystal structures of chalcone O-methyltransferase and isoflavone O-methyltransferase complexed with the reaction products.5 Structures of these and other enzymes are obviously important for the development of biomimetic and thus environmentally more friendly approaches to natural product synthesis. 

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