Vitamin B2 riboflavin

Riboflavin has a central role as a redox coenzyme in energy-yielding metabolism and a more recently discovered role as the prosthetic group of the cryptochromes in the eye - the blue-sensitive pigments that are responsible for day-length sensitivity and the setting of circadian rhythms. 

Dietary deficiency is relatively widespread, yet is apparently never fatal there is not even a clearly characteristic riboflavin deficiency disease. In addition to intestinal bacterial synthesis of the vitamin, there is very efficient conservation and reutilization of riboflavin in tissues. Flavin coenzymes are tightly enzyme bound, in some cases covalently, and control of tissue flavins is largely at the level of synthesis and catabolism of flavin-dependent enzymes. 

Reoxidation of reduced flavin coenzymes is the major source of oxygen radicals in the body, and riboflavin is also capable of generating reactive oxygen species nonenzymically. As protection against this, there is very strict control over the body content of riboflavin. Absorption is limited, and any in excess of requirements is rapidly excreted. 

In bacteria, flavin adenine dinucleotide (FAD) is the prosthetic group of the photolyases that catalyze reductive repair of light-induced pyrimidine dimers in DNA. Riboflavin is the light-emitting molecule in some bioluminescent fungi and bacteria, and is the precursor for synthesis of the dimethylbenzimidazole ring of vitamin B12 (Section 10.7.3). 

The ribityl moiety is not linked to the isoalloxazine ring by a glycosidic linkage, and it is not strictly correct to call FAD a dinucleotide. Nevertheless, this trivial name is accepted, as indeed is the even less correct term flavin mononucleotide for riboflavin phosphate. 

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ViTAMiN B2 (RiBOFLAViN) HAS A CENTRAL ROLE iN ENERGY-YIELDING METABOLISM... 

Riboflavin (E101). This is vitamin B2. Riboflavin can be extracted from yeast but is normally encountered as a nature identical substance. Unfortunately, riboflavin has an intensely bitter taste. The colour produced is an orange yellow. It is stable to acid but is unstable in water. Riboflavin is sometimes used for panned goods. 

Nutritional Folate deficiency Iron deficiency Vitamin Bi (thiamine) deficiency Vitamin B2 (riboflavin) deficiency Vitamin Bg (pyridoxine) deficiency Vitamin B12 (cyanocobalamin) deficiency... 

Vitamin B2 (riboflavin) has the active forms FAD and FMN. It functions in electron trans fer. A deficiency of riboflavin is rare, but it causes dermatitis and angular stomatitis. There is no known toxicity. 

VITAMIN B2 (Riboflavin). Some earlier designations for this substance included vitamin G, lactoflavin, hepatoflavin, ovoflavin, veidoflavin. The chemical name is 6,7-dimcthyl-9-d-l ribityl isolloxazine. Riboflavin is a complex pigment with a green fluorescence. Riboflavin deficiency frequently accompanies pellagra and the typical lesions of both nicotinic acid and riboflavin deficiency are found in that disease. See also Niacin. 

Flavin adenine dinucleotide (FAD) (fig. 10.8) and flavin mononucleotide (FMN) are the coenzymatically active forms of vitamin B2, riboflavin. Riboflavin is the NI0-ribityl isoalloxazine portion of FAD, which is enzymatically converted into its coenzymatic forms first by phosphorylation of the ribityl C-5 hydroxy group to FMN and then by ade-nylylation to FAD. FMN and FAD are functionally equivalent coenzymes, and the one that is involved with a given enzyme appears to be a matter of enzymatic binding specificity. 

Vitamin B2 [riboflavin) Men 1.3 mg/d Women 1.1 mg/d Coenzyme in numerous oxidative metabolic reactions No adverse effects have been reported ... 

Methylenetetrahydrofolate is then reduced to CH3-THF by the vitamin B2 (riboflavin)-dependent enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR), using NADPH as cosubstrate. MTHFR is the key enzyme for diverting 5,10-methylentetrahydrofolate to methylation of homocysteine or to DNA synthesis though the conversion of uracil to thymidine. 

The water soluble vitamins, B2(riboflavin), Biascorbic acid) provided a very interesting study. The spectra for B12 and some of its analogs were first reported by Williams et al., [58] and consist of very strong Cotton bands across almost the entire visible spectral range, Figure 3. 

Pyrazines. In the thirties, the attention on pyrazines was focused on its industrial role in dyes, photographic emulsions and chemotherapy. Its importance in life processes was indicated in its derivative, vitamin B2 (riboflavin, 6,7-dimethyl-9-(l -D-ribityl isoalloxazine). Later,in the midsixties, it was identified in foods and its contributions to the unique flavor and aroma of raw and processed foods attracted the attention of flavor chemists Pyrazine derivatives contribute to the roasting, toasting, nutty, chocolaty, coffee, earthy, caramel, maple-like, bread-like, and bell pepper notes in foods. The reader is referred to the reviews on Krems and Spoerri (88) on the chemistry of pyrazines, and the review of pyrazines in foods by Maga and Sizer (89, 90) Table XVI summaries sensory description and threshold of selected pyrazines. 

De novo fermentation has long been the method of choice for the manufacture of many natural L-amino acids, such as glutamic acid and lysine, and hydroxy acids such as lactic and citric acids. More recently, de novo fermentation is displacing existing multistep chemical syntheses, for example in the manufacture of vitamin B2 (riboflavin) and vitamin C. Other recent successes of white... 

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