Pyridoxine riboflavin function

The water-soluble vitamins comprise the B complex and vitamin C and function as enzyme cofactors. Fofic acid acts as a carrier of one-carbon units. Deficiency of a single vitamin of the B complex is rare, since poor diets are most often associated with multiple deficiency states. Nevertheless, specific syndromes are characteristic of deficiencies of individual vitamins, eg, beriberi (thiamin) cheilosis, glossitis, seborrhea (riboflavin) pellagra (niacin) peripheral neuritis (pyridoxine) megaloblastic anemia, methyhnalonic aciduria, and pernicious anemia (vitamin Bjj) and megaloblastic anemia (folic acid). Vitamin C deficiency leads to scurvy. 

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

The water-soluble vitamins generally function as cofactors for metabolism enzymes such as those involved in the production of energy from carbohydrates and fats. Their members consist of vitamin C and vitamin B complex which include thiamine, riboflavin (vitamin B2), nicotinic acid, pyridoxine, pantothenic acid, folic acid, cobalamin (vitamin B12), inositol, and biotin. A number of recent publications have demonstrated that vitamin carriers can transport various types of water-soluble vitamins, but the carrier-mediated systems seem negligible for the membrane transport of fat-soluble vitamins such as vitamin A, D, E, and K. 

The B-group is a heterogeneous collection of water-soluble vitamins, most of which function as co-enzymes or are precursors of co-enzymes. The B-group vitamins are thiamin, riboflavin, niacin, biotin, pantothenic acid, pyridoxine (and related substances, vitamin B6), folate and cobalamin (and its derivatives, vitamin B12). 

Vitamins are chemically unrelated organic compounds that cannot be synthesized by humans and, therefore, must must be supplied by the diet. Nine vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins (vitamins A, D, K, and E) are termed fat-soluble (Figure 28.1). Vitamins are required to perform specific cellular functions, for example, many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism. In contrast to the water-soluble vitamins, only one fat soluble vitamin (vitamin K) has a coenzyme function. These vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine, and significant quantities are stored in Die liver and adipose tissue. In fact, consumption of vitamins A and D in exoess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds. 

Vitamins are required for satisfactory development or function of most yeasts. Wickerham (177) devised a complete yeast medium which included eight vitamins biotin, pantothenic acid, inositol, niacin, p-aminobenzoic acid, pyridoxine, thiamine, and riboflavin. The concentrations of these growth factors varied widely with inositol in the greatest concentration and biotin in trace amounts. Many of these vitamins are considered major growth factors for yeast multiplication and development, as noted in several studies and reviews (178, 179, 180, 181, 182). Generally, the benefit of adding vitamins to musts and wines has not been established as a normal winery practice. This lack of response is because vitamins occur naturally in sufficient quantities in grapes and are produced by yeasts themselves (3). 

Determination of the effective functioning of particular enzymes or metabolic pathways potentially may be useful in demonstrating adequacy of provision. Enzymes in plasma that may be helpful in this regard are glutathione peroxidase as an index of selenium status, and red cell enzymes, such as transketolase (thiamine), glutathione reductase (riboflavin) or transaminase (pyridoxine), or glutathione peroxidase (selenium) are all widely used. Methyltetrahydrofolate reductase is involved in metabolism of homocysteine, hence assessment of plasma homocysteine is a useful measure of... 

Most vitamins function either as a hormone/ chemical messenger (cholecalciferol), structural component in some metabolic process (pantothenic acid), or a coenzyme (phytonadi-one, thiamine, riboflavin, niacin, pyridoxine, biotin, folic acid, cyanocobalamin). At least one vitamin has more than one biochemical role. Vitamin A as an aldehyde (retinal) is a structural component of the visual pigment rhodopsin and, in its acid form (retinoic acid), is a regulator of cell differentiation. The precise biochemical functions of ascorbic acid and a-tocopherol still are not well defined. 

In 1936, a growth-promoting factor termed vitamin B was isolated from bovine (cow) milk. There are now several different types of vitamin B known and chemically characterized, and they are collectively described as B complex vitamins because of relative similarities in their properties, physiological functions, and distribution in natural resources. Mostly recognized as coenzymes, the eight B complex vitamins currently include Bj (thiamine), B2 (riboflavin), niacin (nicotinamide), B (pyridoxine), pantothenic acid, biotin, B22 (cyanocobalamin), and folacin (folic acid). 

Vitamers are chemically similar substances that have a qualitatively similar vitamin activity. Thus, vitamin D refers to ergocalciferol (Da) and cholecalciferol (D3) and sometimes to their 25-hydroxy- and 1,25-dihydroxy derivatives (Chapter 37). Similarly, pyridoxine (pyri-doxol), pyridoxal, and pyridoxamine are vitamin Be vitamers, riboflavin is the active form of vitamin Ba and cobalamin is vitamin Bia- The members of a particular vitamin family are functionally interchangeable and protect against deficiency symptoms for that vitamin. A vitamin and its corresponding deficiency disease are related as follows ... 

One has only to think of the extraordinarily varied metabolic functions of thiamine, riboflavin, pantothenic acid, pyridoxine, and biotin to realize that it is most unlikely that ascorbic acid could possibly replace every one of these. Moreover, one would have to postulate a quite different mechanism for the large number of other substances, such as sorbitol, sorbose, arabitol, and starch, which spare B vitamins even more readily than ascorbic acid, but which do not have its redox properties. 

Most media contain water-soluble B vitamins. Common to many formulations are vitamins Bi (thiamine), B2 (riboflavin), B3 (niacinamide), Bj (pantothenic acid). Be (pyridoxine), and Bg (folic acid). Biotin (vitamin H), cyanocobalamin (vitamin B]2 ), and ascorbic acid (vitamin C) are also common vitamin components. Although choline and inositol are classically grouped with vitamin components, in cell culture they function as metabolic substrates rather than as catalysts. 

Vitamins are a well-known group of compounds that are essential for human health. Water-soluble vitamins include folate (vitamin B9) to create DNA. Folate also plays an important role in preventing birth defects during early pregnancy. Thiamine is the first vitamin of the B-complex (vitamin Bl) that researchers discovered. It allows the body to break down alcohol and metabolize carbohydrates and amino acids. Like many other B vitamins, riboflavin (vitamin B2) helps the body to metabolize carbohydrates, proteins, and fat. Niacin (vitamin B3) protects the health of skin cells and keeps the digestive system functioning properly. Pantothenic acid (vitamin B5) and biotin allow the body to obtain energy from macronutrients such as carbohydrates, proteins, and fats. Vitamin B6 (pyridoxine) acts as a coenzyme, which means it helps chemical reactions to take place. It also plays a vital role in the creation of nonessential amino acids. 

FIGURE 5.8 Correlation coefficient as a function of resolution for L-ascorbic acid a, thiamine b, nicotinamide c, riboflavin d, and pyridoxine e. 

The vitamin B complex contains a number of factors which are closely associated in their distribution in nature and have related functions in intermediate metabolism. Of the eleven factors which are available in pure form, five have been shown to be constituents of coenzymes, namely, thiamine, riboflavin, niacinamide, pyridoxine, and pantothenic acid. It seems likely that other B vitamins may be found to function in a similar manner. Two members of the B complex, choline and inositol, appear to have lipotropic activity, and two others, folic acid and vitamin B12, have antianemic properties. Deficiency of vitamins of the B complex is one of the most frequently encountered syndromes of malnutrition in man. 

Riboflavin, also called vitamin B2, is stmcturally composed of an isoafloxazine ring with a ribityl side chain at the nitrogen at position 10. This vitamin functions metabol-icafly as the essoitial component of two flavin coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), complexed with proteins, which act as intmnediaries in transfers of electrons in biological oxidation-reduction reactions. Both FAD and FMN function as coenzymes for flavoproteins of flavoenzymes. Flavoproteins are essoitial for the metabolism of carbohydrates, amino acids, and lipids and for pyridoxine and folate conversion to their respective coenzyme forms. 

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