Pyridoxine Transamination

Bg (pyridoxine) Transamination reactions, especially of amino acids Section 23.4... 

Most amino acids lose their nitrogen atom by a transamination reaction in which the -NH2 group of the amino acid changes places with the keto group of ct-ketoglutarate. The products are a new a-keto acid plus glutamate. The overall process occurs in two parts, is catalyzed by aminotransferase enzymes, and involves participation of the coenzyme pyridoxal phosphate (PLP), a derivative of pyridoxine (vitamin UJ. Different aminotransferases differ in their specificity for amino acids, but the mechanism remains the same. 

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... 

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. 

The association between vitamin B6 deficiency and transamination emerged from 1945 when Schlenk and Fisher noted that pyridoxine-deficient rats had a diminished capacity for transamination. In the same year Gunsalus and his colleagues found transamination in Streptococcus faecalis depended on pydridoxal phosphate. The properties of the heat-stable component in purified glutamic-oxaloacetate transaminase were similar to those of pydridoxal phosphate. Later pyri-doxal phosphate was established as an essential coenzyme in many amino acid transformations. 

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. 

Vitamin Bg is a mixture of six interrelated forms pyridoxine (or pyridoxol) (Figure 19.23), pyri-doxal, pyridoxamine, and their 5 -phosphates derivatives. Interconversion is possible between all forms. The active form of the vitamin is pyridoxal phosphate, which is a coenzyme correlated with the function of more than 60 enzymes involved in transamination, deamination, decarboxylation, or desulfuration reactions. 

Be Pyridoxine Coenzyme in transamination Disorders of amino acid... 

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 ... 

The coenzyme form of pyridoxine is known as pyridoxal phosphate (PP) The most common type of reaction requiring PP as a coenz5mie is transamination. Enzymes catalysing such reactions are known as transaminases or aminotransferases. The coenzyme binds to its apoenzyme via Schiff s base between its aldehyde group and the epsilon amino group of a lysine in the... 

Vitamin B complex is the collective term for a number of water-soluble vitamins found particularly in dairy products, cereals and liver.Vitamin B (thiamine) is used by mouth for dietary supplement purposes and by injection in emergency treatment of Wernicke-Korsakoff syndrome. Vitamin B2 (riboflavin) is a constituent of the coenzyme FAD (flavine adenine dinucleotide) and FMN (flavine mononucleotide) and is therefore important in cellular respiration. Vitamin Be (pyridoxine) is a coenzyme for decarboxylases and transamination, and is concerned with many metabolic processes. Overdose causes peripheral neuropathy. It may be used medically for vomiting and radiation sickness and for premenstrual tension. Pyridoxine has a negative interaction with the therapeutic use of levodopa in parkinsonism by enhancing levodopa decarboxylation to dopamine in the periphery, which does not then reach the brain. The antitubercular drug isoniazid interferes with pyridoxine, and causes a deficiency leading to peripheral neuritis that may need to be corrected with dietary supplements. Vitamin B ... 

Figure 8.35. Pyridoxine phosphate-catalyzed transamination and decarho lation.

Another B complex vitamin effected is Be (pyridoxine). This vitamin is required for transaminations ana decarboxylations, two processes of major importance in the metabolism of the central nervous tissue. B0 dehciency occurs in many bodily disorders, dermatitis, anemia, and epileptic seizures, to name some. In alcoholics it is most often seen in delirium tremens (an alcohol withdrawal symptom). 

Transamination reactions require the coenzyme pyridoxal-5 -phosphate (PLP), which is derived from pyridoxine (vitamin B6). PLP is also required in numerous other reactions of amino acids. Examples include racemizations, decarboxylations, and several side chain modifications. (Racemizations are reactions in which mixtures of l- and D-amino acids are formed.) The structures of the vitamin and its coenzyme form are illustrated in Figure 14.2. 

Pyridoxal phosphate (PLP) transamination, amino arid decarboxylation vitamin Be, (pyridoxine)... 

The structure of pyridoxal phosphate, the coenzyme required for all transamination reactions, and pyridoxine, vitamin Bg, the vitamin from which it is derived. 

In pathway A (Figure 1), observed in Pseudomonas MA-1, pyridoxal (2) is produced either from pyridoxamine (15) by a transamination reaction with pyruvate catalyzed by pyridoxamine pyruvate transaminase,or from pyridoxine (1) by an oxidation reaction catalyzed by the FAD-dependent... 

Bg, pyridoxine of NAD and its phosphorylate, NADP assists in hydrogen transfer of glycolysis, fatty acid synthesis, and tissue respiration Nitrogen metabolism transamination,... 

Pyridoxine (vitamin B5) Pyridoxal phosphate (PLP) Dec arboxylation Transamination Racemization —C bond cleavage a,B-Elimination -Substitution Anemia... 

Pyridoxal phosphate is derived from pyridoxine (vitamin Bg). Pyridoxal phosphate is the cofactor not only for transamination reactions but also for decarboxylations and a number of other reactions involving amino acids. 

Vitamins can be divided into two classes, depending upon the significance of their deficiencies. In affluent countries, deficiencies of thiamin, riboflavin, niacin, ascorbic acid, and folic acid are relatively common but of marginal health significance, while in many parts of the world, deficiencies of these substances are significant and life-threatening. Deficiencies in pyridoxine, pantothenic acid, biotin, vitamin B,2, and the fat-soluble vitamins A, D, E, and K are rare. Because pyridoxine is required for transaminations, required amounts depend upon the quantity of protein in the diet. Biotin, pantothenic acid, and vitamin B,2 are ordinarily not required in the diet. However, a deficiency in vitamin B,2 occasionally occurs, and must be treated by injections of the purified vitamin. 

Vitamin Bg exists as six separate forms in the pyridine group of water-soluble vitamins. The common forms are pyridoxal and pyri-doxamine together with their corresponding phosphate esters and pyridoxine forms. These compounds function as cofactors in a wide variety of enzyme reactions, but most notably in the transamination reaction of amino acid biosynthetic pathways. Extraction of this group of vitamins can be performed by the same methods as those described for the B2 vitamins (Section 11.8.3.3). 

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). 

The major sales form of vitamin B6 is the hydrochlorid salt of the primary alcohol pyridoxine. Another vitamin B6 form introduced in the market is the dihydrochlo-rid salt of pyridoxamine. Both vitamin B6 forms are commercially produced via various straightforward chemical synthesis routes. The biologically active cofactor is the aldehyde pyridoxal-5 -phosphate, which is derived in human or animals from the vitamin B6 forms by oxidation or transamination before or after 5 phosphorylation by pyridoxal kinases. 

Pyridoxine Nicotinic acid Pyridoxal phosphate Coenzyme for transamination, decarboxylation and racemization... 

Pyridoxal 5 -phosphate (PLP) is the active form of vitamin B6 (pyridoxine (PN) or pyridoxal (PL)) and an essential cofactor for a large number of enzymes that catalyze a multitude of reactions, including decarboxylation, deamination, racemization, and transamination [1],... 

In the first path, the PLP precursor pyridoxine 5-phosphate (PNP) is biosynthesized from 3-hydroxy-1-aminoacetone phosphate 1 and DXP 2 (Figure 6.1). DXP 2 is formed from pyruvate 3 and glyceraldehyde 3-phosphate 4, catalyzed by deoxy-D-xylulose 5-phosphate synthase (DXS). The 3-hydroxy-1-aminoacetone phosphate 1 is obtained from the erythrose 4-phosphate 5 in four steps. The first step involves the oxidation of erythrose 4-phosphate 5, mediated by erythrose 4-phosphate dehydrogenase (GapB), to erythronate 4-phosphate 6. The latter is further oxidized by D-erythronate 4-phosphate dehydrogenase (PdxB) to 3-hydroxy-4-phosphohydroxy-a-ketobutyrate 7. Transamination reaction between... 

Vitamin is pyridoxal (ll.lOSf), pyridoxine (ll.lOSg) or pyridoxamine (ll.lOSh), all of which exist as their phosphate esters. This vitamin was first isolated in 1936. Pyridoxyl phosphate (ll.lOSi) is a versatile coenzyme used by all living organisms which participates in transamination (11.111) and (11.112), decarboxylation (11.113) and racemisation (11.114) reactions. It is the essential cofactor in amino acid metabolism. Virtually all enzymes which catalyse reactions of 2-amino acids utilise pyridoxyl phosphate as the coenzyme (11.111) through (11.114). 

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