Pyrroloquinoline Quinone PQQ and Tryptophan Tryptophylquinone TTQ

PQQ and TTQ (see Figure 9.6) are the cofactors for a number of dehydrogenases in gram-negative microorganisms. They can undergo reversible reduction to

pyrroloquinoline quinone (PQQ) topaquinone (TPQ)

lysyl tyrosylquinone (LTQ) tryptophanyl tryptophylquinorie (TTQ)

Figure 9.6. Quinone catalysts.

lysyl tyrosylquinone (LTQ) tryptophanyl tryptophylquinorie (TTQ)

Figure 9.6. Quinone catalysts.

the semiquinone and quinol, and can therefore function as electron transport cofactors in redox reactions.

PQQ is present as a noncovalently bound coenzyme in bacterial enzymes, and organisms that are incapable of its de novo synthesis can import it from the culture medium. It is synthesized by reaction between glutamate and tyrosine residues in a small (24 amino acid) peptide that is coded for by one of the bacterial genes known to be required for PQQ synthesis (Stites et al., 2000b).

No mammalian enzymes have been shown to utilize PQQ or TTQ as a cofac-tor, although there is some evidence PPQ may be a dietary essential. Mice fed a defined diet completely devoid of PQQ show impaired growth, friable skin with hemorrhages, hunched posture, decreased fertility, and fewer mitochondria, which are less viable in vitro than normal. These abnormalities are corrected by providing 1 nmol (300 ng) of PQQ per g diet (Stites et al., 2000a). It is not known how much PQQ may normally be present in foods, nor how much may be synthesized by intestinal bacteria.

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