Pyridoxine 4-pyridoxic acid

Solvent System (v/v) Pyridoxal Pyridoxine Pyridoxic Acid Pyridoxic Acid Lactone Pyridoxamine Pyridoxal Phosphate... 

Be Pyridoxine, pyridoxal, pyridoxamine Coenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase role in steroid hormone action Disorders of amino acid metabolism, convulsions... 

Six compounds have vitamin Bg activity (Figure 45-12) pyridoxine, pyridoxal, pyridoxamine, and their b -phosphates. The active coenzyme is pyridoxal 5 -phos-phate. Approximately 80% of the body s total vitamin Bg is present as pyridoxal phosphate in muscle, mostly associated with glycogen phosphorylase. This is not available in Bg deficiency but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids. 

FIGURE 10.2 Structural formula of vitamin and related compounds. 1 — pyridoxine, 2 — pyridoxal, 3 — pyridoxamine, 4 — 4-pyridoxic acid 5 — pyridoxal-5 -phosphate. 

The steroids aldosterone, cortisone, cortisol, 11-P-hydroxyandrostenedione, corticosterone, and rostenedione, 11-desoxycorticosterone, 17-hydroxy-progesterone, and progesterone have been performed on Ultrasphere ODS using methanokwater.19 Ranitidine N-[2-[[[5-[(dimethylamino)methyl]-2-furanyl]-methyl]thio]ethyl]-N1-methyl-2-nitro-l,l-ethenediamine has been separated using a p-Bondapak C18 column operated with acetoni-trile methanol water buffered with triethylamine phosphate.117 Pyridoxal-5 -phosphate and other B6 vitamers, including pyridoxamine phosphate, pyri-doxal, pyridoxine, and 4-pyridoxic acid, were separated as bisulfite adducts... 

Vitamin Ba (pyridoxine, pyridoxal, pyridoxamine) like nicotinic acid is a pyridine derivative. Its phosphorylated form is the coenzyme in enzymes that decarboxylate amino acids, e.g., tyrosine, arginine, glycine, glutamic acid, and dihydroxyphenylalanine. Vitamin B participates as coenzyme in various transaminations. It also functions in the conversion of tryptophan to nicotinic acid and amide. It is generally concerned with protein metabolism, e.g., the vitamin B8 requirement is increased in rats during increased protein intake. Vitamin B6 is also involved in the formation of unsaturated fatty acids. 

Vitamin B6 is a collective term for pyridoxine, pyridoxal, and pyridox amine, all derivatives of pyridine. They differ only in the nature of the functional group attached to the ring (Figure 28.10). Pyridoxine occurs primarily in plants, whereas pyridoxal and pyridoxamine are found in foods obtained from animals. All three compounds can serve as precur sors of the biologically active coenzyme, pyridoxal phosphate. Pyridoxal phosphate functions as a coenzyme for a large number of enzymes, par ticularly those that catalyze reactions involving amino acids. 

Pyridoxine, HC1 is more stable than pyridoxamine and pyridoxal. Acidic aqueous solutions of vitamin Bg are stable definitely at room temperature and may be heated at 120° for 30 minutes without decomposition (13). 

Pyridoxine, pyridoxal, and pyridoxamine, which occur in foodstuffs, are collectively known as vitamin Bg. In the body, all three are converted to pyridoxal phosphate which is the coenzyme for amino-acid decarboxylase and for transaminase. The structures of the three active forms of vitamin Bg and the pyridoxal phosphate, are shown below (55). 

Although, owing to the wide distribution of vitamin Bg in nature, clinical deficiency symptoms are seldom observed, there is little doubt that pyridoxine is essential in human nutrition. Pyridoxine is absorbed from the gastrointestinal tract and is converted to the active form pyri-doxal phosphate. Absorption is decreased in gastrointestinal diseases and also in subjects taking isoniazid (3). It is excreted in the urine as 4-pyridoxic acid (2). The metabolism of vitamin Bg in human beings has been investigated (56). 

Moller (57) has recognized pyridoxine, pyridoxal, pyridoxa-mine, and 4-pyridoxic acid as the excretion products of vitamin Bg. Complete balance studies have been made in pigs and in babies on all the known vitamin Bg metabolic compounds. In babies, the total output exceeded the intake. The assumption that a limited synthesis of vitamin Bg occurs seems justifiable. 

Lumeng et al. (58) have reported the plasma content of Bg vitamers and its relationship to hepatic vitamin Bg metabolism. Orally ingested pyridoxine is rapidly metabolised in liver and its products are released into the circulation in the form of pyridoxal phosphate, pyridoxal, and pyridoxic acid. 

Quantification. High Pressure Liquid Chromatography. In plasma or urine pyridoxine, pyridoxal and 4-pyridoxic acid, sensitivity 300 ng/ml for plasma, 500 ng/ml for urine, UV detection—W. J. O Reilly eta/., 7. Chromat., 1980,183, Biomed. Appl, 9, 492-498. 

Figure 9.1. Interconversion of the vitamin Be vitamers. Pyridoxal kinase, EC 2.7.1.38 pyridoxine oxidase, EC 1.1.1.65 pyridoxamine phosphate oxidase, EC 1.4.3.5 and pyridoxal oxidase, EC 1.1.3.12. Relative molecular masses (Mr) pyridoxine, 168.3 (hydrochloride, 205.6) pyridoxal, 167.2 pyridoxamine, 168.3 (dihydrochloride, 241.1) pyridoxal phosphate, 247.1 pyridoxamine phosphate, 248.2 and 4-pyridoxic acid, 183.2.

Pyridoxal-5-Phosphate Pyridoxine Pyruvic Acid Ribose Sarin Serine Sorbic Acid Sorbitol Stearic Acid Succinic Anhydride Succinimide Sucrose Testosterone Tetrahydrofuran Threonine Toluene... 

Vitamin Bf, (pyridoxine, pyridoxal, and pyridox-amine) is a coenzyme that prefers the world of amino acid metabolism, it is the prosthetic group for all transaminases. Amino acid transamination is a particularly important function. For instance ... 

Aksenova and Messineva (A2) investigated the excretion of 4-pyridoxic acid in 63 patients affected by different forms of leukemia and hypoplastic anemia. Since all pyridoxine derivatives are oxidized to 4-pyridoxic acid, such a compound was considered an index of vitamin Be balance. These patients showed a deficiency of pyridoxine, which increased with simultaneous loadings of tryptophan and pyridoxine (A2). 

Xanthurenic acid and N -methylnicotinamide were measured before and after a standard DL-tryptophan load of 0.54 mg/kg, whereas xanthurenic acid and 4-pyridoxic acid were determined before and after parenteral pyridoxine hydrochloride (25 mg) plus the standard DL-tryptophan load. 

Gershoff and Prien (G6) found that normal subjects excrete significantly less xanthurenic acid and 4-pyridoxic acid and more citric acid than patients with chronic formation of calcium oxalate. A marked rise in excretion of calcium oxalate followed administration of tryptophan in these patients, whereas ingestion of pyridoxine was followed by a decrease in urinary oxalate. 

TLC of vitamin Be compounds, on various layers in different solvents, was studied. The Rf values of pyri-doxine, pyridoxal, pyridoxamine, pyridoxal ethyl acetate, 4-pyridoxic acid, 4-pyridoxic acid lactone, pyridoxine phosphate, pyridoxal phosphate, and pyridoxamine phosphate were 0.62, 0.68, 0.12, 0.54, 0.91, 0.91, 0.95, 0.95, and 0.86, respectively, by TLC on silica gel HF254 with... 

Pyridoxine Hydrochloride, USP. Pyridoxine hydrochloride.. S-hydroxy-6-methyl-3.4-pyridinedimethanol hydrochloride. vitamin B, hydrochloride, rat antidermatitis factor. is a white, odorless, crystalline substance that is soluble l .S in water and 1 100 in alcohol and in.soluble in ether. It is relatively. stable to light and air in the solid form and in acid solutions at a pH no greater than S. at which pH it can be autoclaved at IS pounds at I20°C for 20 to 30 minutes. Pyridoxine is unstable when irradiated in aqueous solution.s at pH 6.8 or above. It is oxidized readily by hydrogen peroxide and other oxidizing agents. Pyridoxine is as stable in mixed vitamin preparations as riboflavin and nicotinic acid. A 1% aqueous solution has a pH of 3. The pK i values fur pyridoxine. pyridoxal. and pyridoxamine are S.OO. 4.22. and 3.40. respectively, and their pK 2 values are 8.96. 8.68. and 8.05. respectively. 

Metabolic Role. Riboflavin coenzymes are required for most oxidations of carbon-carbon bonds (Fig. 8.29). Examples include the oxidation of succinyl CoA to fumarate in the Krebs cycle and introduction of a,jS-unsaturation in /3-oxidation of fatty acids. Riboflavin is also required for the metabolism of other vitamins, including the reduction of 5,10-methylene tetrahydrofolate to 5-methyl tetrahydrofolate (Fig. 8.49), and interconversion of pyridoxine-pyridoxal phos-phate-pyridoxamine (Fig. 8.33). Because oxi-dation/reductions that use FAD or FMN as the coenzyme constitute a two-step process, some flavin coenzyme systems contain more than one FAD or FMN. 

Uptake and Metabolism. The vitamin Bg family consists of pyridoxine, pyridoxal, pyridoxamine, pyridoxine phosphate, pyridoxal phosphate (PLP), and pyridoxamine phosphate (Fig. 8.33). The commercial form is pyridoxine. Pyridoxal phosphate is the coenzyme form. It and pyridoxamine phosphate are from animal tissues. Pyridoxine is from plant tissues. All phosphorylated forms are hydrolyzed in the intestinal tract by phosphatases before being absorbed passively. Conversion to the phosphorylated forms occurs in the liver. Notice that niacin (NAD) and riboflavin (FMN, FAD) are required for interconversion among the vitamin Bq family. The phosphorylated forms are transported to the cells where needed. The major excretory product is 4-pyr-idoxic acid. 

Pyridoxic Acid, 3-Hydroxy-5-(hydroxymethyl)-2-meihyl-4-pyridinecar boxy lie acid 3-hydroxy-5-(hydroxy-methyl)-2-methylisonicotinic acid 2 -methyl-3 -hydroxy -4-carboxy-5-hydroxymethylpyridine. CgHjNO, mol wt 183,16. C 52.46%, H 4.95%, N 7.65%, O 34.94%. Occurs in urine. It is the chief metabolic product of pyridoxine pyridoxal, and pyridoxamine. Isoln from human urine Singal, Sydenstricker, Science 78, 545 (1941). Isoln and synthesis Huff, Perlzweig, J. Biol Chem ]S5, 345 (1944). 

The vitamin Be group of coenzymes consists of pyridoxine, pyridoxal, and pyridoxamine and their metabolically active phosphorylated forms. They are striking for the variety of enzymic reactions in which they are important, and many amino acid transformations, including various transaminations and decarboxylations, are vitamin B dependent. Compounds with vitamin B activity are apparently not stored in the body in large amounts, and biochemical evidence of B deficiency can develop quickly if intake is inadequate (S4). 

Hydrolysis of pyridoxal phosphate to pyridoxal followed by oxidation to 4-pyridoxic acid is the major catabolic pathway for vitamin B6 in most mammalian species. In cats, however, the major urinary metabolites are pyridoxine 3-sulfate and N-methylpyridoxine (Cobum and Mahuren, 1987). Also, in humans receiving very large vitamin B6 intakes excretion of 5-pyridoxic acid may become significant (Mahuren et aL, 1991). 

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