FAD-dependent enzymes

The FAD-dependent enzyme glutathione reductase plays a role in the antioxidant system. Glutathione reductase restores reduced glutathione (GSH), the most important antioxidant in erythrocytes, from oxidized glutathione (GSSG) [1, 2]. 

The oxidation of fatty acids within the Knoop-Lynen cycle occurs in the matrix. The Knoop-Lynen cycle includes four enzymes that act successively on acetyl-CoA. These are acyl-CoA dehydrogenase (FAD-dependent enzyme), enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase (NAD-dependent enzyme), and acetyl-CoA acyltrans-ferase. Each turn, or revolution, of the fatty acid spiral produces... 

This FAD-dependent enzyme [EC 1.4.3.3] catalyzes the reaction of a D-amino acid with dioxygen and water to generate an a-keto acid, ammonia, and hydrogen peroxide. Substrate specificity is wide and includes glycine. 

This FAD-dependent enzyme [EC 1.14.13.9], also called kynurenine 3-monooxygenase, catalyzes the reaction of kynurenine with NADPH and dioxygen to produce 3-hydroxykynurenine, NADP, and water. 

Methylenetetrahydrofolate reductase (NADPH) [EC 1.5.1.20] is an FAD-dependent enzyme that catalyzes the reaction of 5-methyltetrahydrofolate with NADP to produce 5,10-methylenetetrahydrofolate and NADPH. 5,10-Methylenetetrahydrofolate reductase (FADH2) [EC 1.7.99.5] is an FAD-dependent enzyme that catalyzes the reaction of 5-methyltetrahydrofolate with an acceptor to produce 5,10-methylenetetrahydrofolate and the reduced acceptor. 

This FAD-dependent enzyme [EC 1.6.2.2], also known as cytochrome bs reductase, catalyzes the reaction of NADH with two molecules of ferricytochrome bs to produce NAD and two ferrocytochrome bs. 

This enzyme [EC 1.6.1.1] (also known as NAD(P)+ trans-hydrogenase (B-specific), pyridine nucleotide transhy-drogenase, and nicotinamide nucleotide transhydro-genase) catalyzes the reversible reaction of NADPH with NAD+ to produce NADP+ and NADH. This FAD-dependent enzyme is B-specific with respect to both pyridine coenzymes. In addition, deamino coenzymes will also serve as substrates. 

Nitrite reductase (NAD(P)H) [EC 1.6.6.4] catalyzes the reaction of three NAD(P)H with nitrite to yield three NAD(P)+, NH4OH, and water. Cofactors for this enzyme include FAD, non-heme iron, and siroheme. (2) Nitrite reductase (cytochrome) [EC 1.7.2.1] is a copper-depen-dent system that catalyzes the reaction of nitric oxide with two ferricytochrome c and water to produce nitrite and two ferrocytochrome c. (3) Ferredoxin-nitrite reductase [EC 1.7.7.1], a heme- and iron-dependent enzyme, catalyzes the reaction of ammonia with three oxidized ferredoxin to produce nitrite and three reduced ferredoxin. (4) Nitrite reductase [EC 1.7.99.3] is a copper- and FAD-dependent enzyme that catalyzes the reaction of two nitric oxide with an acceptor substrate and two water to produce two nitrite and the reduced acceptor. 

This FAD-dependent enzyme [EC 1.5.99.8] catalyzes the reaction of L-prohne with an acceptor and water to produce (5)-l-pyrrohne 5-carboxylate and the reduced acceptor. 

ACTIN ASSEMBLY KINETICS BIOCHEMICAL SELF-ASSEMBLY FAD-dependent enzymes,... 

Polyamine oxidase (amine oxygen oxidoreductase, deaminating, flavin-containing), is also a FAD-dependent enzyme and has many similarities to MAO. It is responsible for the oxidation of the secondary amino group in such substrates as A/-acetyl spermine and spermidine in the biosynthesis of spermidine and putrescine [1,12], This enzyme will not be covered in this chapter. 

D-Amino acid oxidase D-Amino acids (see p. 5) are found in plants and in the cell walls of microorganisms, but are not used in the synthesis of mammalian proteins. D-Amino acids are, hew ever, present in the diet, and are efficiently metabolized by 1he liver. D-Amino acid oxidase is an FAD-dependent enzyme that catalyzes the oxidative deamination of these amino acid isomers. The resulting a-ketoacids can enter the general pathways of amino acid metabolism, and be reaminated to L-isomers, or cafe balized for energy. 

Monoamine oxidase (MAO) serves as a marker enzyme for outer membrane. There is some MAO activity in the inner membrane and therefore also in SMPs however, a high level of monoamine oxidase in the SMP preparation indicates a large contamination by outer membrane. Mitochondrial monoamine oxidase is an FAD-dependent enzyme that catalyzes the oxidation of amines to aldehydes (Equation E10.2). A convenient assay for this enzyme uses benzylamine as substrate and monitors the rate of ben-zaldehyde production at 250 nm. 

Nitrite reduction in assimilatory nitrate-reducing Neurospora crassa, Torulopsis nitratophila, Azotobacter vinelandii, and Azotobacter chro-ococcum appears to be catalyzed by enzyme systems which require flavin and metals. The enzyme from N. crassa has been partially purified, and its molecular weight has been estimated to be 300,000 (344, 346, 351, 367). The enzyme reduces both nitrite and hydroxylamine to ammonia and utilizes NADH or NADPH as electron donor. It is reported to be a FAD-dependent enzyme and to contain iron, copper, and active thiol (346, 367). Three moles of NADH are oxidized per mole of nitrite reduced to ammonia. It has been suggested that the reduction of nitrite occurs in three steps, each involving two electrons. Thus, hyponitrite and hydroxylamine have been proposed as successive intermediates in the re-... 

Because flavin coenzymes are widely distributed in intermediary metabolism, the consequences of deficiency maybe widespread. Because riboflavin coenzymes are involved in the metabohsm of folic acid, pyridoxine, vitamin K, and niacin, deficiency will affect enzyme systems other than those requiring flavin coenzymes. With increasing riboflavin deficiency, tissue concentrations of FMN and FAD fall, as does flavokinase activity, thus further decreasing FMN concentrations. FMN concentrations are decreased proportionally more than FAD concentrations. Decreases in the activities of enzymes requiring FMN generally follow the fall in tissue concentrations, whereas the FAD-dependent enzymes are more variably affected. ... 

The aliphatic alcohol oxidase, a FAD-dependent enzyme, catalyzes the oxidation of primary short-chain alcohols to the corresponding aldehydes. Dioxygen can be replaced by synthetic acceptors such as dichlorophenolindophenol or phenazine methosulfate [147l... 

Many FAD-dependent enzymes catalyzing these reactions are found in bacteria and fungi, either in pathways allowing them to metabolize hydrocarbons or in pathways that synthesize secondary metabolites such as antibiotics." " " There has been long-standing interest in using these enzymes for enantioselective chemical syntheses, either as purified enzymes or expressed in engineered microbes for bioreactors. 

One carrier system that has been extensively studied in insect flight muscle is the glycerol-phosphate shuttle. This mechanism uses the presence on the outer face of the inner mitochondrial membrane of an FAD-dependent enzyme... 

A peculiar sugar modification occurs in the biosynthesis of the aclacino-mycins. These anthracyclines contain a trisaccharide moiety attached to the aklavinone scaffold at the C-7 position (Scheme 1). The first two carbohydrates in the aclacinomycins are rhodosamine and 2-deoxyfucose, but they differ structurally in their third sugar component, which is rhodinose in AclN, cinerulose A in AclA, L-aculose in AclY and cinerulose B in AclB [157]. The conversion of rhodinose to L-aculose is catalysed in a two-step process by the FAD-dependent enzyme aclacinomycin oxidoreductase [71] (Scheme 5, step 31). The three-dimensional structure of this oxidase revealed that the cofactor FAD is bound via two covalent bonds to the enzyme. Crystal structure and functional data further established a mechanism where the two different reactions are catalysed in the same active site of the enzyme but by different active site residues [71]. 

---