Flavin Dehydrogenase Action

Oxidative phosphorylation begins with the entiy of electrons into the respiratory chain. Most of these electrons arise from the action of dehydrogenases that collect electrons from catabolic pathways and funnel them into universal electron acceptors—nicotinamide nucleotides (NAD+ or NADP+) or flavin nucleotides (FMN or FAD). 

Acyl-CoA dehydrogenase is a flavin-linked, membrane-bound enzyme, associated with the mitochondrial respiratory complexes. When FADH2 is produced, it is oxidized by the respiratory chain (Chap. 14). Hydroxyacyl-CoA dehydrogenase is in the mitochondrial matrix, and the NADH produced by the action of this enzyme on hydroxyacyl-CoA compounds contributes to the pool of NADH in the matrix. It is also oxidized by the respiratory chain (Chap. 14). 

Oi-, OH or OH+), a similar mode of action can be taken into consideration for the native flavoproteins. The specific action of different flavin oxidases, dehydrogenases and hydroxylases can most likely be attributed to specific proteins which are bound with the flavin moiety and are in a position to dictate the particular breakdown of HFIOOH. For example, the oxidases were thought to react specifically, yielding oxidized flavin and H2O2, while the dehydrogenases were supposed to yield both flavin and superoxide radicals (HF1- + HO 2)- The hydroxylases were assumed to account for the reaction of one of the activated oxygen intermediates with the respective substrate. 

In spite of the fact that succinic dehydrogenase has been known to exist for half a century and that many laboratories have attempted to study its mode of action, little is known of its mode of regulation. The 23 amino acids adjacent to the flavin have been sequenced. 

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