Redox enzymes quinone containing

Quinone containing redox enzymes are a much less widely studied group, and to date fewer examples have been characterized. The prosthetic group in this case is a quinone, pyrrolo-quinoline quinone (PQQ), and again it is a two-electron... 

Further examples of recycling enzyme pairs include copper enzymes such as laccase and tyrosinase which oxidizes a wide range of substances including catecholamines, phenols, and redox dyes by dissolved oxygen in combination with flavoenzymes, haem-, and pyrroloquino-line quinone containing (NADTf independent) dehydrogenases. 

The transformation of the mussel adhesive protein to glue involves a sequence of chemical events in which timing is a critical element. The redox enzyme (catechol oxidase) plays an important role. Recently, Waite has observed that the catechol oxidase is present at very high concentrations in ribbed mussels. At these concentration levels, it acts more like a reagent than a catalyst. Waite has also established that the enzyme shows an apparent molecular weight of 38 kDa and does not contain any metal atoms. Presumably it possesses a quinone cofactor at levels as high as one quinone/mg of enzyme. 

Gregg BA, Heller A. Redox polymer films containing enzymes. 1. A redox conducting epoxy cement—synthesis, characterization, and electrocatalytic oxidation of hydro-quinone. J Phys Chem 1991 95 5970-5975. 

Oxidation of P-nicotinamide adenine dinucleotide (NADH) to NAD+ has attracted much interest from the viewpoint of its role in biosensors reactions. It has been reported that several quinone derivatives and polymerized redox dyes, such as phenoxazine and phenothiazine derivatives, possess catalytic activities for the oxidation of NADH and have been used for dehydrogenase biosensors development [1, 2]. Flavins (contain in chemical structure isoalloxazine ring) are the prosthetic groups responsible for NAD+/NADH conversion in the active sites of some dehydrogenase enzymes. Upon the electropolymerization of flavin derivatives, the effective catalysts of NAD+/NADH regeneration, which mimic the NADH-dehydrogenase activity, would be synthesized [3]. 

A number of enzymes contain other carbonyl compounds that catalyze reactions in the same way as does pyridoxal phosphate or that catalyze redox reactions. Such compounds include pyruvate (Section 9.8.1) pyrroloquino-line quinone, which may be a dietary essential (Section 9.8.2) and a variety... 

The enzyme has been first purified by Enoch and Lester and recently shown by X-ray analysis to be a 510-kDa membrane-bound complex of (a/3y)3 structure. It chatmels the electrons withdrawn from formate by the a-subunit, which is a selenopolypeptide of 110-kDa molecular mass via 11 redox centers consisting of molybdopterin-guanine dinucleotides and five Fe4S4 centers in a single unbranched chain to two heme b groups in the y-subunit, which also contains a quinone binding site. The formate-binding site is located at the periplasmic side, the quinone reduction site at the opposite side of the cytoplasmic membrane. 

In correlation with the nature of compounds that can induce ARE-driven transcription, many of the proteins whose expression is mediated by the ARE have an endogenous role in regulating cellular redox status and protecting the cell from oxidative damage. Enzymes such as GST, NQOl, and HO-1 function to detoxify harmful by-products of oxidative stress, including lipid and DNA base hydroperoxides (29,30), quinones (31), and heme-containing molecules (32). The induction of enzymes involved in GSH biosynthesis leads to an increase in cellular GSH levels that provides a buffer against oxidative insult (2). 

Redox proteins that include quinone cofactor units play important roles in biological ET processes. Some of the quinoproteins include the quinone cofactor in a non-covalently linked configuration, such as the pyrroloquinoline quinone, PQQ, dependent enzymes, whereas other quinoproteins include the quinone cofactor covalently-linked to the protein, for example topaquinone (2,4,6-trihydroxyphenylalanine quinone, TPQ) dependent enzymes. A number of quinoproteins include in addition to the quinone cofactor an ET cofactor unit in another protein subunit. These cofactors may be metal ions or a cytochrome-type heme cofactor such as D-fructose dehydrogenase that is a heme containing PQQ-dependent enzyme. ... 

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