P450 Systems

Cyt P450 systems are also involved in many other metabolic processes—e.g., the biosynthesis of steroid hormones (see p. 172), bile acids (see p. 314), and eicosanoids (see p. 390), as well as the formation of unsaturated fatty acids (see p. 409). The liver s reddish-brown color is mainly due to the large amounts of P450 enzymes it contains. 

Cytochrome P450-dependent mono oxygenases reactions 3 

Cyt P450-dependent monooxygenases catalyze reductive cleavage of molecular oxygen 

The course of Cyt P450 catalysis is in principle well understood. The most important function of the heme group consists of converting molecular oxygen into an especially reactive atomic form, which is responsible for all of the reactions described above. 

Koolman, Color Atlas of Biochemistry, 2nd edition 2005 Thieme All rights reserved. Usage subject to terms and conditions of license. 

These are found in bacteria, fungi, and yeasts, and mediate important hydroxylations. 

Reference should be made to reviews that discuss mechanistic aspects of cytochrome P450 reactions (Guengerich 1990), the reactions mediated by both enkaryotic and prokaryotic cytochrome 

Class II Three-component system of prokaryotic systems 

FIGURE 3.17 Cytochrome P450 systems in prokaryotes and eukaryotes. (From Neilson, A.H. and Allard, A.-S. Microbial metabolism of PAHs and heteroarenes, The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, 1998. With permission.) 

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Mitochondrial cytochrome P450 systems are found in steroidogenic tissues such as adrenal cortex, testis, ovary, and placenta and are concerned with the biosyn-... 

Lipids are also components of the cytochrome P450 system. The preferred lipid is phosphatidylcholine, which is the major lipid found in membranes of the endoplasmic reticulum. 

P450 systems (Sariaslani 1991), their widespread role in the transformation of xenobiotics (Smith and Davis 1968), and their occurrence and activities in yeasts (Kappeli 1986). The essential features of prokaryotic and eukaryotic cytochrome P450 systems are compared in Figure 3.17. 

Unusual aspects of bacterial cytochrome P450 systems are worth pointing out ... 

The hydroxylation of steroids at various positions is carried out by a range of fungi, and probably involves the cytochrome P450 system (Breskvar and Hudnik-Plevnik 1977). 

The aerobic degradation of cycloalkanes has been examined in both monocyclic and polycyclic snb-strates. In all of them, monooxygenation is the first step and this is sometimes accomplished by cytochrome P450 systems. Reviews of the degradation of alicyclic componnds inclnding monoterpenes... 

Monooxygenation mediated by the cytochrome P450 system of Streptomyces has been observed in oxaarenes ... 

Cytochrome P450 System - Drug-metabolizing Enzymes... 

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