Vitamins B6 and

Riboflavin is one of the B vitamins. It is also known as vitamin B6 and is made up of carbon, hydrogen, nitrogen, and oxygen atoms. When 10.00 g of vitamin B6 is burned in oxygen, 19.88 g of C02 and 4.79 g of H20 are obtained. Another experiment shows that vitamin B6 is made up of 14.89% N. What is foe simplest formula for vitamin Be ... 

Severe hypochromic microcytic anemia, responding only to vitamin B6 and not to iron, a typical symptom of B6 deficiency in many species of animals, is related to the dependence of porphyrin biosynthesis on vitamin Be, preceding the 8-aminolevulinic acid stage, at the condensation of glycine with succinate to yield a-amino- 3-ketoadipate, the immediate precursor of 8-aminolevulinic acid. 

Structures of vitamin B6 and and the anti-tuberculosis drug isoniazid. 

Figure 22-2 The glyceraldehyde 3-phosphate pyruvate alternative pathway of isoprenoid biosynthesis. The intermediate 1-deoxyxylulose 5-phosphate may enter terpenes, vitamin B6, and thiamin. Isopentenyl diphosphate is shown as the final product, but the intermediate steps are uncertain. See Lange et al 2 ...

When present in excess methionine is toxic and must be removed. Transamination to the corresponding 2-oxoacid (Fig. 24-16, step c) occurs in both animals and plants. Oxidative decarboxylation of this oxoacid initiates a major catabolic pathway,305 which probably involves (3 oxidation of the resulting acyl-CoA. In bacteria another catabolic reaction of methionine is y-elimination of methanethiol and deamination to 2-oxobutyrate (reaction d, Fig. 24-16 Fig. 14-7).306 Conversion to homocysteine, via the transmethylation pathway, is also a major catabolic route which is especially important because of the toxicity of excess homocysteine. A hereditary deficiency of cystathionine (3-synthase is associated with greatly elevated homocysteine concentrations in blood and urine and often disastrous early cardiovascular disease.299,307 309b About 5-7% of the general population has an increased level of homocysteine and is also at increased risk of artery disease. An adequate intake of vitamin B6 and especially of folic acid, which is needed for recycling of homocysteine to methionine, is helpful. However, if methionine is in excess it must be removed via the previously discussed transsulfuration pathway (Fig. 24-16, steps h and z ).310 The products are cysteine and 2-oxobutyrate. The latter can be oxidatively decarboxylated to propionyl-CoA and further metabolized, or it can be converted into leucine (Fig. 24-17) and cysteine may be converted to glutathione.2993... 

An example of a biologically important aldehyde is pyridoxal phosphate, which is the active form of vitamin B6 and a coenzyme for many of the reactions of a-amino acids. In these reactions the amino acid binds to the coenzyme by reacting with it to form an imine of the kind shown in the equation. Reactions then take place at the amino acid portion of the imine, modifying the amino acid. In the last step, enzyme-catalyzed hydrolysis cleaves the imine to pyridoxal and the modified amino acid. 

LC Rail, SN Meydani. Vitamin B6 and immune competence. Nutr Rev 51 217-225, 1993. 

DA Sampson, Q-B Wen, K Lorenz. Vitamin B6 and pyridoxine glucoside content of wheat and wheat flours. Cereal Chem 73 770-774, 1996. 

Pyridoxal-5 -phosphate is the coenzyme form of vitamin B6, and has the structure shown in figure 10.3. The name vitamin B6 is applied to any of a group of related compounds lacking the phosphoryl group, including pyridoxal, pyridoxamine, and pyridoxine. 

Schiff base formation can have a considerable effect on both the position and degree of activation of the coordinated amino acid. The Schiff bases derived from amino acids and pyridoxal have attracted considerable attention due to the biochemical significance of vitamin B6 and the realization that many of the enzymic reactions involving B6 could be brought about in the absence of enzyme by using pyridoxal and various metal ions.444,445,461 4 2,342... 

Model reactions have contributed significantly to our understanding of biological processes. Both pyridoxal phosphate (vitamin B6) and Bi2-coenzymes have proved useful in mechanism studies. Methyl transfer reactions to various metals are of environmental significance. In 1968 it was shown that methylcobalamin could transfer a methyl carbanion to mercury(II) salts in aqueous solutions. Recent research on interaction between B12-coenzymes and platinum salts has shown that charged Ptn salts labilize the Co—-C bond. Secondly, the B12-coenzymes are unstable in the presence of platinum salts this observation correlates with the fact that patients who have received cw-platin develop pernicious anemia. 

Contains modest amounts of niacin, folate, vitamin B6, and some minerals... 

As shown in the review of the homocysteine metabolism, vitamin B 2, vitamin B6, and folate are important cofactors in the metabolic pathways for homocysteine elimination, and consequently, deficiencies of these vitamins are characterized by elevated plasma concentrations of tHcy. Hyperhomocysteinemia is also frequently found in diseases such as renal failure, rheumatic and auto-immune diseases, hypothyroidism, and malignancies. Several drugs are also known to increase plasma tHcy concentrations (16-24). 

Carmody et al. found that the addition of homocysteine to a culture of vascular smooth muscle cells resulted in a dose-dependent increase in DNA synthesis and cell proliferation, but vitamins B6 and B 2 alone did not substantially inhibit the effect of homocysteine. However, the addition of folic acid resulted in significant inhibition of DNA synthesis (64). Rosiglitazone has been shown to reduce serum tHcy levels, smooth muscle proliferation, and intimal hyperplasia in Sprague-Dawley rats fed a diet high in methionine (65). 

In the Heart Outcomes Prevention Evaluation 2 (HOPE-2) study, 5522 patients aged 55 or older with vascular disease or diabetes were randomized to treatment with either placebo or a combination 2, 5 mg of folic acid, 50 mg vitamin B6, and I mg vitamin B 2, for an average of five years. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, and stroke. Mean plasma homocysteine levels decreased by 2.4 jimol/L in the treatment group and increased by 0.8 jimol/L in the placebo group. The primary outcome occurred in 18.8% of patients assigned to active therapy and in 19.8% of those assigned to placebo (relative risk = 0.95 95% Cl = 0.84-1.07 P = 0.41) (68). 

The a-amino groups are removed from amino acids by a process called transamination. The acceptor for this reaction is usually the a-keto acid called a-ketoglutarate which results in the formation of glutamate and the corresponding a-keto acid. The coenzyme of all transaminases is pyridoxal phosphate which is derived from vitamin B6 and which is transiently converted during transamination into pyridoxamine phosphate. 

Isoniazid was developed in 1951 as a result of the observation that vitamin B6 was weakly active against the bacterium that causes tuberculosis. Isoniazid has a related structure to vitamin B6 and acts by stopping the production of substances used by the bacteria for the growth of cell... 

Folic acid is one of the B vitamins. Research has established that consuming about 800 micrograms by way of foods and supplements, along with vitamins B6 and B12, reduces levels of the amino acid homocysteine, another risk factor for heart disease. Now recent... 

Teratogenic activity has been attributed to doxylamine, a constituent of many combinations with vitamin B6 and antispasmodic agents, and used in the treatment of hyperemesis gravidarum. However, extensive studies and reviews have suggested that the incidence of malformations is not higher in children whose mothers have taken formulations containing antihistamines as a group, and in particular the combination of doxylamine/pyridoxine with or without dicycloverine (100-102). 

Jansen T, Romiti R, Kreuter A, Altmeyer P. Rosacea ful-minans triggered by high-dose vitamins B6 and B12. J Eur Acad Dermatol Venereol 2001 15(5) 484-5. 

In chapter 3, we briefly discussed the link between elevated homocysteine levels, increased acidity, and, ultimately, cardiovascular problems. While additional studies are required, promising scientific evidence suggests that folate (also known as vitamin Bg), vitamin B6, and vitamin BI2 are effective at lowering homocysteine levels and may ultimately play a role in reducing vascular disease. In addition, research has revealed an inverse relationship between folate and the occurrence of colorectal cancer.5 (In other words, the more deficient in folate you are, the greater your risk of colorectal cancer.)... 

Selhub J. Folate, vitamin B12 and vitamin B6 and one carbon metabofism. J Nutr Health Aging 2002 6 39-42. 

Tarr JB, Tamura T, Stokstad EL. Availability of vitamin B6 and pantothenate in an average American diet in man. Am J Clin Nutr 1981 34 1328-37. 

The vitamin content (Table 1.9) is also interesting, because QS have high levels of vitamin B6 and total folate, whose amounts in 100 g can cover the requirements of children and adults. The riboflavin content in 100 g contributes 80% of the daily needs of children and 40% of those of adults (National Academy of Sciences, 2004). The niacin content does not cover the daily needs, but is beneficial in the diet. Thiamin values in quinoa are lower than those in oat or barley, but those of niacin, riboflavin, vitamin B6, and total folate are higher (Ranhotra et al., 1993 USDA, 2005). 

Biosynthesis of vitamin B6 and structurally related derivatives 01MI10. Historical development and recent synthetic innovations in the total synthesis of cobyric acid, a vitamin B12 precursor 03EJ030. 

Fig. 3 Structures of the molecules involved in the glycogenolysis process. Here PLP is a derivative of vitamin B6 and serves as prosthetic group for GP PLP is apprehended at the active site by a Schiff base linkage, formed by reaction of the aldehyde of PLP with the 8-amino group of a Lys residue...

---