Pyridoxine/pyridoxal/pyridoxamine

Vitamin B6. Figure 1 Structure of pyridoxin, pyridoxal, pyridoxamine, and the coenzymes pyridoxal-5 -phosphate and pyridoxamine-5Y-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. 

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. 

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. 

TLC of vitamin Bg compounds, on various layers in different solvents, was studied. The Rf values of pyridoxine, 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 0.2% NH4OH in water as solvent. When adsorbents containing fluorescent indicators are used, all forms and derivatives of vitamin Bg can be detected... 

Pyridoxine, pyridoxal, pyridoxamine, pyridoxal phosphate, pyridoxamine phosphate, and 4-pyridoxic acid were baseline resolved and detection limits of -C1 pmol were obtained on a C g column (A = 328nm, ex 393 nm, em) using a 0/100 -> 100/0 (at lOmin hold lOmin) IPA/water (33mM phosphate buffer pH 2.2 with lOmM octanesulfonic acid) gradient [327]. Excellent quantitative results from spinal fluid samples were also obtained. 

Pyridoxine, pyridoxal, pyridoxamine, pyridoxal phosphate, and pyridoxamine phosphate were extracted from cooked sausage and separated on a 35°C deactivated base C 8 column (A = 290nm, ex 395 nm, em) using a 99/1 water (50 mM KH2PO4 buffer at pH 3.2)/acetonitrile mobile phase [1585]. Very good peak shapes and resolution were achieved and elution was complete in 4 min. Linear ranges were reported as 10-500 pg injected and detection limits of 0.02-0.5 mg/100 g sample were cited (analyte dependent). 

Pyridoxine (vitamin Be) was first recognized as an essential factor in animal nutrition. Later it was found to have growth-promoting ability for various strains of bacteria, yeast, molds, fungi, and plants. Snell, in a series of studies with bacteria, noted variations in response to certain natural extracts as source of Be among several bacteria. Out of this work came the appreciation that vitamin Be existed in several different forms to which various test organisms responded differently. The vitamin Be complex is now known to consist of the following compounds pyridoxine, pyridoxal, pyridoxamine, and the phosphorylated forms of the two latter substances. 

At the present time, 9 fractions of the vitamin B complex are generally recognized, and others are postulated. Those discussed in this book (alphabetically under their name designations) are biotin, choline, folacin (folic acid), niacin (nicotinic acid nicotinamide), pantothenic acid (vitamin B-3), riboflavin (vitamin B-21), thiamin (vitamin B-1), vitamin B-6 (pyridoxine, pyridoxal pyridoxamine), and vitamin B-12 (cobalamins). 

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

The usable range for T. pyriformis is from 0.3-300 mug/ml. The organism utilizes pyridoxal, pyridoxamine pyridoxine, and pyridoxal-5-phosphate. Pyridoxamine + pyridoxal yielded the best growth approximately 120 times more pyridoxine is required to yield the same growth as pyridoxamine (Fig. 4). As with nicotinic acid and its amide, when these compounds are added together in the same concentration, the increment of growth is less than the sum of the individual increments. Upon an intramuscular load dose of 100 mg of pyridoxine, peak vitamin Bs levels are reached 2 hours after injection. The curves for 4 normal individuals are illustrated in Fig. 5. 

Vitamin Bg a family of molecules having vitamin Be activity these include pyridoxal, pyridoxine, and pyridoxamine precursors to the coenzyme pyridoxal phosphate. 

We have just noted the role that pyridoxal phosphate plays as a coenzyme (cofactor) in transamination reactions (see section 15.6). Pyridoxal 5 -phosphate (PLP) is crucial to a number of biochemical reactions. PLP, together with a number of closely related materials that are readily converted into PLP, e.g. pyridoxal, pyridoxine and pyridoxamine, are collectively known as vitamin Bg, which is essential for good health. 

This enzyme [EC 2.7.1.35] (also known as pyridoxine kinase, pyridoxamine kinase, and vitamin kinase) catalyzes the reaction of ATP with pyridoxal to produce ADP and pyridoxal 5 -phosphate. Pyridoxine, pyridoxamine, and various other derivatives can also act as substrates. 

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. 

Biotin-Containing Enzymes. 2. The Mechanism of Biotin Action 738 Box 14-C The Vitamin B6 Family Pyridoxine, Pyridoxal, and Pyridoxamine... 

PN = pyridoxine PM = pyridoxamine PL = pyridoxal PNP = pyridoxine phosphate PMP = pyridoxamine phosphate PLP = pyridoxal phosphate PNG = 5 -0-(/8-D-glucopyranosyl)pyri-doxine. 

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. 

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). 

Wada and Snell (150) have developed a method for the assay of pyridoxine and pyridoxamine phosphate, based on enzymatic oxidation to pyridoxal which is allowed to react with phenylhydrazine. 

Three enzymes play an active role in the metabolism of vitamin B6 in human erythrocytes. Pyridoxal kinase uses ATP to phosphorylate pyridoxine, pyri-doxamine, and pyridoxal. Pyridoxamine oxidase oxidizes pyridoxamine-5 -phosphate and pyridoxine-5 -phosphate to pyridoxal-5 -phosphate. The phosphatase activity produces pyridoxal from pyridoxal-5 -phosphate. The assay of the three enzymes required separation of the semicarbazone derivatives of pyridoxal-5 -phosphate and pyridoxal. The mobile phase used by Ubbink and Schnell (1988) contained 2.5% acetonitrile. Detection was by fluorescence. 

All three forms of vitamin B6 [pyridoxal, pyridoxine, and pyridoxamine] are phosphorylated by a single kinase that uses ATP as the phosphate donor. This assay describes the use of pyridoxamine as the substrate. 

The phosphorylated vitamers are dephosphorylated by membrane-bound alkaline phosphatase in the intestinal mucosa pyridoxal, pyridoxamine, and pyridoxine are all absorbed rapidly by carrier-mediated diffusion. Intestinal mucosal cells have pyridoxine kinase and pyridoxine phosphate oxidase (see Figure 9.1), so that there is net accumulation of pyridoxal phosphate by metabolic trapping. Much of the ingested pyridoxine is released into the portal circulation as pyridoxal, after dephosphorylation at the serosal surface. 

Kelsay J, Baysal A, and Linkswiler H (1968a) Effect of vitamin Bg depletion on the pyridoxal, pyridoxamine and pyridoxine content of the blood and urine of men. Journal of Nutrition 94, 490-4. 

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. 

Chemical Name Pyridoxine Chemical Abstracts Services Registry Numbers CAS 58-56-0 CAS 65-23-6 Synonyms Vitamin Pyridoxal Pyridoxamine Adermine hydrochloride 3,4-Pyridinedimethanol 5-Hydroxy-6-methyl hydrochloride Chemical/Pharmaceutical/Other Class Water-soluble vitamin... 

Pyridoxine (pyridoxol), pyridoxamine, and pyridoxal are the three natural forms of vitamin Bg. They are converted to pyridoxal phosphate, which is required for the synthesis, catabohsm, and interconversion of amino acids. 

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. 

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