Flavo-dehydrogenase substrates

Other substrates for flavo-dehydrogenases include structures with electron-withdrawing (activating) groups next to the position of dehydrogenation. Such reactions appear to be initiated by abstraction of the relatively acidic a-hydrogen atom by a basic residue (e.g. His), thus involving a carbanion of the substrate as an intermediate or a transition state. 

I. 6.99.3]. NADH dehydrogenase [EC 1.6.99.3] catalyzes the reaction of NADH with an acceptor to produce NAD+ and the reduced acceptor. Iron-sulfur and flavo-proteins are still being used as cofactors with this component of EC 1.6.5.3. Interestingly, after certain preparations have been followed, cytochrome c may serve as the acceptor substrate. 

Quinoprotein dehydrogenases containing PQQ or TTQ have been shown to function in various microorganisms in addition to the NAD(P)-dependent and flavo-protein dehydrogenases. The PQQ-containing dehydrogenases require Ca (or Mg) for structural as well as catalytic purposes. However, the mechanism of activation of PQQ, the substrate or the hemiketal adduct by the metal ion, is still unknown. 

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