Flavoenzyme-based

Figure 1. Structures of redox polymers used as electron relay systems in flavoenzyme-based biosensors. Shown are siloxane (top), ethylene oxide (middle), and branched siloxane-ethylene oxide (bottom) polymers.

Amperometric biosensors cells, 3-5 development, 2-3 flavoenzyme-based, 111-112 mediators, 3-4... 

Purine nucleotides are degraded by a pathway in which they lose their phosphate through the action of 5 -nucleotidase (Fig. 22-45). Adenylate yields adenosine, which is deaminated to inosine by adenosine deaminase, and inosine is hydrolyzed to hypoxanthine (its purine base) and D-ribose. Hypoxanthine is oxidized successively to xanthine and then uric acid by xanthine oxidase, a flavoenzyme with an atom of molybdenum and four iron-sulfur centers in its prosthetic group. Molecular oxygen is the electron acceptor in this complex reaction. 

Flavoenzymes constitute about 2% of all biological catalysts and are classified in several ways. One classification is based on EC number (enzyme nomenclature) and refers to the type of reaction catalyzed. More sophisticated classifications concern the inclusion of sequence, fold, and function. Historically, a distinction is made between simple and complex flavoenzymes (4). The latter proteins contain besides flavin other cofactors like heme, tetrahydrobiopterin, and metal ions. 

The flavoenzyme UDP-galactop)ranose mutase (UGM) plays a key role in the cell wall biosynthesis of many pathogens, including Mycobacterium tuberculosis. McNeil and co-workers developed a microtiter plate assay for UGM (O Scheme 14) [157]. The assay is based on the release of tritiated formaldehyde from UDP-galactofuranose but not UDP-galactopyranose by periodate and was used to identify a uridine-based enzyme inhibitor from a chemical library. The potent inhibitor 320KAW73 (IC50 = 6 pM) was identified. 

In this review, the simple flavoenzymes will be discussed in groups according to the chemistry of a halfreaction - usually the biologically important half-reaction. This is different from the usual classifications based on the net reactions catalyzed or structural motifs. In addition to these enzymes, there are several flavoproteins that do not fit easily into any chemical group. These enzymes will be discussed at the end and include examples where more than one type of chemical conversion occurs, the enzyme contains additional prosthetic groups such as metal centers, or there is no evidence for the flavin being involved chemically in the reaction. 

Two main UV lesions that form on DNA are cyclobutane pyrimidine dimers and 6-4 photoadducts. 6-4 photolyase uses reduced flavin to correct 6-4 photoadducts. DNA photolyases are flavoenzymes that photochemically reverse pyrimidine dimers formed in DNA by UV irradiation. DNA photolyases are monomeric proteins that have been divided into two classes based on sequence. " Class 1 enzymes are found in many microbes, while Class 2 enzymes have been found in higher organisms including goldfish and... 

Pai and co-workers recently developed a general strategy for determining the stereochemistries of the flavoenzymes that is fundamentally based on the stereochemical features of the glutathione reductase reaction (87, 88). Their experimental approach relies on the observations that (1) the reduced forms of the 8-demethyl-8-hydroxy-5-deazaflavins (7) are not susceptible to nonenzymic racemization,... 

N. Markoglou, R. Hsuesh and I. Wainer, Immobilized enzyme reactions based upon the flavoenzymes monoamine oxidase A and B, J. Chroma-togr., B, 2004, 804, 295-302. 

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