Methanol dehydrogenase reaction mechanism

The Role of Ammonia in the Reductive Half-Reaction Mechanism of Methanol Dehydrogenase... 

The mechanism of the PQQjdependent oxidation of methanol to formaldehyde which is catalyzed by methanol dehydrogenase is shown in Scheme 18. In the reductive half-reaction methanol is converted into formaldehyde with concomitant reduction of PQCJ to the quinol form (53). The exact mechanism of the reductive half-reaction has been controversial and two alternative mechanisms have been proposed. In the... 

Several important homogeneous catalytic reactions (e.g. hydroformylations) have been accomplished in water by use of water-soluble catalysts in some instances water can act as a solvent and as a reactant for hydroformylation. In addition, formation of aluminoxanes by partial hydrolysis of alkylaluminum halides results in very high activity bimetallic Al/Ti or Al/Zr metallocene catalysts for ethene polymerization which would be otherwise inactive. Polymerization of aryl diiodides and acetylene gas has recently been achieved in water with palladium catalysts. Finally, nickel-containing enzymes, such as carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase, operate in water with reaction mechanisms comparable with those of the WGSR or of the Monsanto methanol-to-acetic-acid process. ... 

Similarly to the flavin-dependent reactions, several mechanisms have been discussed, including covalent substrate-PQQ intermediates or hydride transfer1179-1811. The most important QDHs are methanol (alcohol) dehydrogenase (E.C. 1.1.99.8) and glucose dehydrogenase (E. C. 1.1.99.17), which will be discussed briefly. 

The mechanism of liver alcohol dehydrogenase (LADH) has been extensively studied. For a recent overview the reader is referred to Ref [93]. Reaction field effects on the transition structure of model hydride transfer systems have been calculated at ab initio 4-3IG basis set level [93, 94]. The active site of enzymes are usually assumed to be designed to receive molecules in the transition state for the reaction they catalyze. This special sort of surrounding medium effects has been computationally documented recently [95]. From the reaction geodesic passing through the transition state for hybride transfer in the pyridium cation/methanolate model system, only the TS-structure could be fitted into the LADH active site. The normal mode analysis carried out on the TS showed an excellent agreement with isotopic substitution experiments [95]. Reaction field calculations on this model systems have also been performed. For an overview of biomolecular interactions the reader is referred to Ref [96]. 

The removal and use of one-carbon units from folate Single-carbon units are removed from folate by a number of reactions. The enzyme 10-formylTHF dehydrogenase provides a mechanism for disposing of excess one-carbon units as carbon dioxide. (Folate administration to animals enhances the conversion of ingested methanol and formate to carbon dioxide, diminishing methanol toxicity.) Additionally, singlecarbon units from 10-formylTHF are used for the biosynthesis of purines (Figure 2). 

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