Monooxygenase enzymes reactions

Monooxygenase enzymes catalyze reactions in which one atom of oxygen derived from dioxygen is incorporated into an organic substrate while the other atom is reduced by two electrons to form water (1,2). 

It is unknown what role is played by ligand environments in proteins and in synthetic analogues in stabilizing different species as it is also unknown which species represent active oxidants capable of transfering oxygen atoms to substrate in the enzyme systems. Moreover, it is not known how a binuclear metal active site might differ tom a mononuclear active site or if there is one type of reaction mechanism that operates in all or most of the monooxygenase enzymes or if each type of enzyme follows a different mechanism. 

Parathion is also metabolized to diethyl phosphorothioic acid and -nitrophenol in a reaction requiring a cytochrome P-4Jg-containing monooxygenase enzyme system (, 4). Studies with H. 0 have indicated that water in addition to molecular oxygen and NADPH is required in this reaction ( ). Diethyl phosphate and -nitro-phenol can also be formed from parathion in a monooxygenase-catalyzed reaction (6). 

For foreign compounds, the majority of oxidation reactions are catalyzed by monooxygenase enzymes, which are part of the mixed function oxidase (MFO) system and are found in the SER (and also known as microsomal enzymes). Other enzymes involved in the oxidation of xenobiotics are found in other organelles such as the mitochondria and the cytosol. Thus, amine oxidases located in the mitochondria, xanthine oxidase, alcohol dehydrogenase in the cytosol, the prostaglandin synthetase system, and various other peroxidases may all be involved in the oxidation of foreign compounds. 

Note that the monooxygenase model reactions described above are performed in non-aqueous diluters. Therefore, hematin form is absent and only hemin is present, of which, apparently, formation of an intermediate shaped as Hm=0 is typical. Model catalysts of cytochrome P-450 operate in liquids, similar to enzymes themselves. Their activity depends on many factors, including diluter origin, reaction mixture pH and cell effects. As indicated [1], the gas-phase version of the oxidation process is much freer from these effects. 

Another class of heme proteins containing iron protoporphyrin as the active center includes enzymes such as cytochrome P-450 and horseradish peroxidase (HRP). The former is a monooxygenase enzyme (MW 50,000) that catalyzes hydroxylation reaction of substrates such as drugs, steroids and carcinogens ... 

These observations have led to the development of a trajectory-based model to rationalize die selectivity of the monooxygenase enzyme in Beauveria sulfurescens, and this may aUow the regio- and stereo-chonistry of transformations on new (related) substrates to be predicted. Also of some assistance in predicting the stereochemical outcome of the reactions is the study of the mechanism, and this has beoi investigated and diown, at least in some cases, to proceed with inversion of stereocheniistry. ... 

These compounds are common in soils and sediments as the products of anaerobic fermentation reactions. Metabolism of these compounds can directly consume O2 (through monooxygenase enzymes) or indirectly, through formation of NADH which is shuttled into oxidative phosphorylation and the electron transport chain. Oxidative metabolism of Ci compounds is an important microbial process in soils and sediments, consuming the methane produced by methanogenesis. 

Since 1985 there has been a great increase in the number of papers describing reactions of dioxiranes. Space limitations will not permit the authors to refer to all of these papers. Instead the authors have attempted to cover all of the different reaction types. Within each type of reaction attempts have been made to indicate the various structure types encompassed by that reaction. This survey of dioxirane reactions indicates that the dioxiranes are excellent mimics of the monooxygenase enzymes <86JA2470>. In this case, mimicry is meant to refer to the range of reaction type and not the mechanistic details of the reactions. Nevertheless, studies of dioxirane reactions may provide some insights into the corresponding enzyme-catalyzed reactions. 

Cytochrome P-450 enzymes are a group of monooxygenase enzymes that oxygenate a wide variety of substrates. Examples of such reactions are ... 

As mentioned above, much less is known about the structural characteristics and mechanisms of the nonheme metal-containing monooxygenase enzymes. From the similarities of the overall stoichiometries of the reactions and the resemblance of some of the enzymes to dioxygen-binding proteins, it is likely that the initial steps are the same as those for cytochrome P-450, i.e., dioxygen binding followed by reduction to form metal-peroxide or hydroperoxide complexes. It is not obvious that the next step is the same, however (i.e., O—O bond cleavage... 

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