Riboflavin, acylation

Group-transfer reactions often involve vitamins3, which humans need to have in then-diet, since we are incapable of realizing their synthesis. These include nicotinamide (derived from the vitamin nicotinic acid) and riboflavin (vitamin B2) derivatives, required for electron transfer reactions, biotin for the transfer of C02, pantothenate for acyl group transfer, thiamine (vitamin as thiamine pyrophosphate) for transfer of aldehyde groups and folic acid (as tetrahydrofolate) for exchange of one-carbon fragments. Lipoic acid (not a vitamin) is both an acyl and an electron carrier. In addition, vitamins such as pyridoxine (vitamin B6, as pyridoxal phosphate), vitamin B12 and vitamin C (ascorbic acid) participate as cofactors in an important number of metabolic reactions. 

Diagnosis of medium-chain acyl-CoA dehydrogenase deficiency in lymphocytes and liver by a gas chromatographic method the effect of oral riboflavin supplementation. 

In laying hens, induction of this riboflavin protein results in a 100-fold increase in plasma riboflavin, compared with males or nonlaying females. In mutant chickens lacking the protein, the adult has massive urinary loss of riboflavin. The embryo develops normally for about 10 days, then develops severe hypoglycemia associated with a reduction in medium-chain acyl coenzyme A (CoA) dehydrogenase to 20% of normal activity and the accumulation of intermediates of fatty acid oxidation (White, 1996). 

Acyl CoA dehydrogenases in fatty acid /S-oxidation. These enzymes are especially sensitive to riboflavin depletion, and riboflavin deficiency is characterized by impaired fatty acid oxidation and organic aciduria (Section 7.4.1). These are also the enzymes affected in riboflavin-responsive organic acidurias. 

Within a day of initiating a riboflavin-free diet in weanling rats, there is a 35% decrease in the oxidation of palmitoyl CoA. All three mitochondrial acyl CoA dehydrogenases are affected, although it is the short-chain acyl CoA... 

Gregersen N, Christensen ME, Christensen E, and Kolvraa S (1986) Riboflavin responsive multiple acyl-CoA dehydrogenation deficiency. Assessment of 3 years of riboflavin treatment. Acta Paediatrica Scandinavica 75, 676-81. 

Veitch K, Draye JP, Van Hoof F, and Sherratt HS (1988) Effects of riboflavin deficiency and clofibrate treatment on the five acyl-CoA dehydrogenases in rat liver mitochondria. 

Riboflavin is also a component of the flavoproteins succinate dehydrogenase and acyl CoA dehydrogenase,... 

Otto Shape s power supplement contains carnitine. However, his body can synthesize enough carnitine to meet his needs, and his diet contains carnitine. Carnitine deficiency has been found only in infants fed a soy-based formula that was not supplemented with carnitine. His other supplements likewise probably provide no benefit, but are designed to facilitate fatty acid oxidation during exercise. Riboflavin is the vitamin precursor of FAD, which is required for acyl CoA dehydrogenases and ETFs. CoQ is synthesized in the body, but it is the recipient in the electron transport chain for electrons passed from complexes I and II and the ETFs. Some reports suggest that supplementation with pantothenate, the precursor of CoA, improves performance. 

Rao, K.V.R. Qureshi, I.A. (1997) Can. J. Physiol. Pharmacol., 75, 423-4360. Decompensation of hepatic and cerebral acyl-CoA metabolism in BALB/cByJ mice by chronic riboflavin deficiency restoration by acetyl-L-camitine. 

Riboflavin is an important constituent of the flavoproteins.The prosthetic group of these compound proteins contains riboflavin in the form of the phosphate (flavin mononucleotide, FMN) or in a more complex form as flavin adenine dinucleotide (FAD). There are several flavoproteins that function in the animal body they are all concerned with chemical reactions involving the transport of hydrogen. Further details of the importance of flavoproteins in carbohydrate and amino acid metabolism are discussed in Chapter 9. Flavin adenine dinucleotide plays a role in the oxidative phosphorylation system (see Fig. 9.2 on p. 196) and forms the prosthetic group of the enzyme succinic dehydrogenase, which converts succinic acid to fumaric acid in the citric acid cycle. It is also the coenzyme for acyl-CoA dehydrogenase. 

One particular case of such pathological conditions is multiple acyl-CoA dehydrogenation deficiency (MADD) or glutaric aciduria type-II, a rare disease arising from defects in either ETF or ETF QO. In this condition, vitamin B2 supplementation has in some cases been successfully employed for the treatment of this fatty add oxidation (FAO) disorder. However, the molecular rational for the benefidal eflect of riboflavin supplementation is not fully clearly defined and the reason why only some MADD patients are responsive to riboflavin whereas others are not remains as one of the key challenging issues in the field (Gregersen et al. 1990 Olsen et al. 2007). 

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