Mechanism monooxygenation

FIGURE 2.4 Proposed mechanism for monooxygenation by cytochrome P450. 

Suske WA, WJH van Berkel, H-P Kohler (1999) Catalytic mechanism of 2-hydroxybiphenyl 3-monooxygen-ase a flavoprotein from Pseudomonas azelaica HBPl. J Biol Chem 274 33355-33365. 

A wide range of mechanisms are involved in the degradation and transformation of aromatic compounds with nitro substituents. These include reduction of the nitro group, and dioxygenation, monooxygenation, and reduction of the aromatic ring. A review devoted to 2,4,6-trinitrotolune is available (Esteve-Nunez et al. 2001). 

The two most important difference spectra of reduced CYP are the well-known CO spectrum, with its maximum at or about 450 nm, and the type III spectrum, with two pH-dependent peaks at approximately 430 and 455 nm. The CO spectrum forms the basis for the quantitative estimation of CYP. The best-known type III ligands for CYP are ethyl isocyanide and compounds such as the methylenedioxyphenyl synergists and SKF 525A, the last two forming stable type III complexes that appear to be related to the mechanism by which they inhibit monooxygenations. 

Methylenedioxy (Benzodioxole) Ring Cleavage. Methylenedioxy-phenyl compounds, such as safrole or the insecticide synergist, piperonyl butoxide, many of which are effective inhibitors of CYP monooxygenations, are themselves metabolized to catechols. The most probable mechanism appears to be an attack on the methylene carbon, followed by elimination of water to yield a carbene. The highly reactive carbene either reacts with the heme iron to form a CYP-inhibitory complex or breaks down to yield the catechol (Figure 7.8). 

Action mechanisms and kinetic features of catalases, peroxidases and monooxygenases. Catalytic system selection for conjugated dehydrogenation, epoxidation and monooxygenation reactions. 

Progress in decoding the mechanism of cytochrome P-450, which catalyzes epoxidation and hydroxylation of various hydrocarbons, has stimulated the search for comparatively simple and effective iron porphyrin systems [20-24], The reaction mechanism of monooxygenation can be illustrated by the following diagram ... 

Intermediate formation mechanisms indicated in the monooxygenation diagram relate to the class of reactions in non-aqueous solvents. This is the reason why the hemin form of iron porphyrin is absent in it. Hence, hemin is present, of which the intermediate formation shaped as Hm+0 (where Hm is heme) is typical. 

Thus, the reaction mechanism of monooxygenation (hydroxylation) consists of oxygen atom transfer from hydrogen peroxide molecule to CH4 molecule by adding OH group to it and simultaneous proton transfer from methane molecule to the matrix. The well-known oxynoid mechanism of monooxygenation is not fulfilled. 

Thus, the adequate kinetic simulation of methane hydroxidation with hydrogen peroxide on PPFe3+OH/AlSiMg mimic, carried out with the help of the Michaelis-Menten equation, indicates high probability of the monooxygenation mechanism suggested [91]. 

It is obvious from the mechanism (9.1)—(9.7) that oxidation condition variation may direct the process towards selective formation of a definite product. For example, oxygen-containing compounds can be obtained in one highly selective stage (monooxygenation) by the reaction channel (9.7). The comparative simplicity of these reactions is also associated with the fact that metal complexes, representing something like weak acids , coordinate weak bases, such as olefins, N2, CO, etc. with formation of unstable complexes, which provide for catalytic transformation of the substrate [5],... 

Boddupalli, S. S., Pramanik, B. C., Slaughter, C. A., Estabrook, R. W., and Peterson, J. A. 1992c. Fatty-Acid Monooxygenation by P450bm-3 Product Identification and Proposed Mechanisms for the Sequential Hydroxylation Reactions. Arch. Biochem. 

The majority of synthetic reactions in mammalian cells takes place in the cytosol. The intramitochondrial localization of transhydrogenase excludes a direct participation in these anabolic processes. Substrate shuttle mechanisms (176, 177) are required to allow for the interaction between intra- and extramitochondrial nicotinamide nucleotide-dependent reactions. In the first instance transhydrogenase can be regarded to be functionally related to intramitochondrial NADP-linked reactions. A number of studies on isolated mitochondria have elaborated these relationships in some detail, in particular with regard to mitochondrial monooxygenation reactions and to the metabolism of glutamate and isocitrate. 

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