Two-Electron-Transferring Flavoprotein Dehydrogenases

The initial step of the two-electron-treinsferring reactions is the removal of a proton from the substrate, followed by the intermediate formation of em adduct between the substrate and prosthetic group at N-5 of the flavin. This undergoes cleavage to yield dihydroflavin tind the oxidized product, which is commonly a carbon-Ccubon double bond. The reduced flavin is then reoxidized by reaction with an electron-trtuisferring flavoprotein, as discussed above, or in some cases by reaction with nicotinamide nucleotide coenzymes. 

The nicotinamide nucleotide independent flavoprotein dehydrogeneises include the following  

Succinate dehydrogenase in the triceuboxylic acid cycle, which reacts directly with ubiquinone in the mitochondrial electron transport cheun. 

Acyl CoA dehydrogenases in fatty acid yS-oxidation. These enzymes eue especially sensitive to riboflavin depletion, and riboflavin deficiency is chtuacterized by impaired fatty acid oxidation and orgtinic aciduria (Section 7.4.1). These tue tdso the enzymes eiffected in riboflavin-responsive orgtinic acidurias. 

Dimethylglycine tind sarcosine dehydrogenases in the catabolism of choline (Section 14.2.1). In these reactions, a methyl group in the substrate is oxidized by FAD, then the intermediate adduct undergoes hydrolysis to release formaldehyde, which reacts with tetreihydrofolate to form 5,10-methylene tetreihydrofolate. 

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