Redox coenzymes flavin mononucleotide

Riboflavin (from the Latin flavus, yellow) serves in the metabolism as a component of the redox coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD see p. 104). As prosthetic groups, FMN and FAD are cofactors for various oxidoreductases (see p. 32). No specific disease due to a deficiency of this vitamin is known. 

Vitamin B2 forms the basis of two coenzymes, flavin mononucleotide (FMN) (Fig. lc). and flavin adenine dinucleotide (FAD) (Fig. Id). Both coenzymes are involved in redox reactions. The general scheme is ... 

Riboflavin and other flavinoids are found in dairy produce and meat and to a lesser extent in cereals. The RDA is 1.6-2.0 mg. Flavins are stable to heat and acid but destroyed by exposure to light. UV irradiation of riboflavin in acid or neutral solution gives rise to the fluorescent compound lumichrome, whereas in alkaline solutions irradiation produces lumiflavin. Flavins are required in the body as their coenzymes flavin mononucleotide and flavin adenine dinucleotide, which are involved in redox reactions involving one- and two-electron transfers and linked to many energy-dependent processes in the body. 

Riboflavin (vitamin Bj) is chemically specified as a 7,8-dimethyl-10-(T-D-ribityl) isoalloxazine (Eignre 19.22). It is a precnrsor of certain essential coenzymes, such as flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) in these forms vitamin Bj is involved in redox reactions, such as hydroxylations, oxidative carboxylations, dioxygenations, and the reduction of oxygen to hydrogen peroxide. It is also involved in the biosynthesis of niacin-containing coenzymes from tryptophan. 

Riboflavin, also known as vitamin B2, is an essential component of FAD and flavin mononucleotide (FMN)—coenzymes tliat are involved in many redox reactions. 

These yellow redox systems all contain the conjugated tricyclic isoalloxazine ring system. Riboflavin, vitamin B2, is an isoalloxazine which is phosphorylated and then adenylated to two active redox coenzyme forms - FMN (flavin adenine mononucleotide, R = phosphorylated ribose) and FAD (flavin adenine dinucleotide, adenylated FMN). 

Oxidoreductase dehydrogenase and flavoenzymes. Nicotinamide adenine dinucleotide (NAD+)/nicotinamide adenine dinucleotide phosphate (NADF) and flavin mononucleotide (FMN)/flavin adenine dinucleotide (FAD) are the two major types of redox coenzymes. 

Instead, biochemical redox reactions involving the oxidation of alkane to alkene require the participation of a coenzyme such as flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). The reduced forms FADH2 and FMNHj act as hydride donors in the alkene hydrogenation reactions (Figure 1.41). 

The energy necessary to generate ATP is extracted from the oxidation of NADH and FADH2 by the electron transport chain, a series of four protein complexes, denoted Complexes I-IV (Fig. 7b). NADH is oxidized by Complex I FADH2 is oxidized by Complex II. Each complex contains multiple redox centers several iron-sulfur proteins and flavin mononucleotide in Complex I, and three iron-sulfur centers and a heme in Complex II. The electrons are then passed to coenzyme Q, which contains an organic redox center. Coenzyme Q transfers the electrons to Complex III. Complex III contains three hemes and... 

Many proteins and another coenzyme called flavin mononucleotide participate in this process, which involves five redox reactions. These redox reactions generate many resonance-stabilized free radicals. 

So what does riboflavin do As such riboflavin does nothing. Like thiamine, riboflavin must undergo metabolic change to become effective as a coenzyme. It fact, it undergoes two reactions. The first converts riboflavin to riboflavin-5-phosphate (commonly known as flavin adenine mononucleotide, FMN), about which we will say no more, and the second converts it to flavin adenine dinucleotide, FAD. The flavins are a class of redox agents of very general importance in biochemistry. FAD is the oxidized form and FADH2 is the reduced form. ... 

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