Vitamins amino acid metabolism

Pyridoxal phosphate is a coenzyme for many enzymes involved in amino acid metabolism, especially in transamination and decarboxylation. It is also the cofactor of glycogen phosphorylase, where the phosphate group is catalytically important. In addition, vitamin Bg is important in steroid hormone action where it removes the hormone-receptor complex from DNA binding, terminating the action of the hormones. In vitamin Bg deficiency, this results in increased sensitivity to the actions of low concentrations of estrogens, androgens, cortisol, and vitamin D. 

If a vitamin or cofactor is involved in amino acid metabolism, it s most likely pyridoxal phosphate (B6), unless it involves serine, and then it s B6 and folic acid. 

A group of enzymes which is particularly important in amino acid metabolism in the liver (and also in muscle) is the transaminases, (also called aminotransferases). These are vitamin B6 (pyridoxine) dependent enzymes which transfer an amino group from an amino acid to an oxo (keto) acid, thus ... 

The importance of nutrition in the dental caries problem is reviewed in 90 pages by Shaw.22 Although we have indicated that metabolic peculiarities in the area of mineral metabolism seem "most likely to be pertinent" to the dental caries problem (p. 218), it does not follow that interest should be restricted to this field. Because teeth are organic structures produced as the result of metabolic processes, there is not a single vitamin, amino acid, or other nutrient factor which may not be implicated in the disease. Probably many different deficiencies are involved in the production of the sum total of all caries existing in all individuals. Much evidence, of course, has been found to indicate the importance of calcium, phosphorus, and vitamin D, but other items may also be very important. 

The vitamin Be family of molecules are metabolic precursors to pyridoxal phosphate, an essential coenzyme for multiple enzymes involved in amino acid metabolism. 

The terminology vitamin Bg covers a number of structurally related compounds, including pyridoxal and pyridoxamine and their 5 -phosphates. Pyridoxal 5 -phosphate (PLP), in particular, acts as a coenzyme for a large number of important enzymic reactions, especially those involved in amino acid metabolism. We shall meet some of these in more detail later, e.g. transamination (see Section 15.6) and amino acid decarboxylation (see Section 15.7), but it is worth noting at this point that the biological role of PLP is absolutely dependent upon imine formation and hydrolysis. Vitamin Bg deficiency may lead to anaemia, weakness, eye, mouth, and nose lesions, and neurological changes. 

The active form of vitamin Be, pyridoxai phosphate, is the most important coenzyme in the amino acid metabolism (see p. 106). Almost all conversion reactions involving amino acids require pyridoxal phosphate, including transaminations, decarboxylations, dehydrogenations, etc. Glycogen phosphory-lase, the enzyme for glycogen degradation, also contains pyridoxal phosphate as a cofactor. Vitamin Be deficiency is rare. 

Dietary deficiency of vitamin ieads to impaired amino acid metabolism in many organs, but the CNS is most severeiy affected. 

In addition to enhancement with essential vitamins, amino acids, and proteins, plants can also be metabolically engineered to produce nutritionally superior carbohydrates and lipids. The relative inexpensiveness as well as the capability to grow large-scale quantities make plant production an attractive feature. In the case of carbohydrates such as starch and sucrose, many products or modifications of these products can be produced on a large scale and at much lower costs than are currently available. For example, trehalose, a food additive, was in the past too costly for large-scale production however, it has now been produced in transgenic tobacco tissue at a much reduced cost. 

Pyridoxal phosphate is the coenzyme for the enzymic processes of transamination, racemization and decarboxylation of amino-acids, and for several other processes, such as the dehydration of serine and the synthesis of tryptophan that involve amino-acids (Braunstein, 1960). Pyridoxal itself is one of the three active forms of vitamin B6 (Rosenberg, 1945), and its biochemistry was established by 1939, in considerable part by the work of A. E. Braunstein and coworkers in Moscow (Braunstein and Kritzmann, 1947a,b,c Konikova et al 1947). Further, the requirement for the coenzyme by many of the enzymes of amino-acid metabolism had been confirmed by 1945. In addition, at that time, E. E. Snell demonstrated a model reaction (1) for transamination between pyridoxal [1] and glutamic acid, work which certainly carried with it the implication of mechanism (Snell, 1945). 

Vitamin B6 Pridoxine Pyridoxamine Pyridoxal Pyridoxal phosphate Cotacior for enzymes, particularly in 1 amino acid metabolism J. 

Vitamin B6 (pyridoxine, pyridoxamine, and pyridoxal) has the active form, pyridoxal phosphate. It functions as a cofactor for enzymes, particularly in amino acid metabolism. Deficiency of this vitamin is rare, but causes glossitis and neuropathy. The deficiency can be induced by isoniazid, which causes sensory neuropathy at high doses. 

Thiamine, biotin and pyridoxine (vitamin B) coenzymes are grouped together because they catalyze similar phenomena, i.e., the removal of a carboxyl group, COOH, from a metabolite. However, each requires different specific circumstances. Thiamine coenzyme decarboxylates only alpha-keto acids, is frequently accompanied by dehydrogenation, and is mainly associated with carbohydrate metabolism. Biotin enzymes do not require the alpha-keto configuration, are readily reversible, and are concerned primarily with lipid metabolism. Pyridoxine coenzymes perform nonoxidative decarboxylation and are closely allied with amino acid metabolism. 

Biochemistry is important in many fields of science in addition to medicine. For instance, biochemists investigate food by studying molecules such as vitamins, amino acids, fatty acids, various minerals, and water, all of which are dietary requirements for healthy nutrition. They also explain how these nutrients are absorbed by the body and what they do in the cells. For example, the question of how the body derives energy from dietary fats and oils involves a series of biochemical reactions explained by the biochemistry of the metabolic pathways. 

Vitamins, cofactors, and metals have the potential to broaden the scope of antibody catalysis considerably. In addition to hydrolytic and redox reactions, they facilitate many complex functional group interconversions in natural enzymes.131 Pyridoxal, for example, plays a central role in amino acid metabolism. Among the reactions it makes possible are transaminations, decarboxylations, racemizations, and (3,y-eliminations. It is also essential for ethylene biosynthesis. Not surprisingly, then, several groups have sought to incorporate pyridoxal derivatives into antibody combining sites. 

Marginal inadequacy, affecting amino acid metabolism and possibly also steroid hormone responsiveness, may be relatively common. A number of vitamin Be dependency syndromes have been reported - inborn errors of metabolism in which the defect is in the coenzyme binding site of the affected enzyme. 

Whereas tetrahydrobiopterin is biosynthesized from GTP via just three enzyme-catalyzed steps (2), some coenzyme biosynthetic pathways are characterized by enormous complexity. Thus, the biosynthesis of vitamin B12 requires five enzymes for the biosynthesis of the precursor uroporhyrinogen III (16) from succinyl-CoA (10) and glycine (11) that is then converted into vitamin B12 via the sequential action of about 20 enzymes (3). Additional enzymes are involved in the synthesis of the building blocks aminopropanol and dimethylbenzimidazole (4, 5). Vitamin B12 from nutritional sources must then be converted to coenzyme B12 by mammalian enzymes. Ultimately, however, coenzyme B12 is used in humans by only two enzymes, albeit of vital importance, which are involved in fatty acid and amino acid metabolism (6). Notably, because plants do not generate corrinoids, animals depend on bacteria for their supply of vitamin B12 (which may be obtained in recycled form via nutrients such as milk and meat) (7). 

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 ... 

Pernicious anemia. Purine biosynthesis is impaired by vitamin Bj2 deficiency. Why How might fatty acid and amino acid metabolism also be affected by a vitamin Bj2 deficiency ... 

Another example of the biosynthesis of a thiazole ring is in enzymatic biosynthesis of thiamin. Thiamin is a thiazole-containing vitamin whose supply in humans relies on diet. It acts as a coenzyme and plays an important role in carbohydrate and amino acid metabolism <2003NPR184>. Thiamin deficiency can be fatal. 

Vitamin B Three substances are classed under the term pyridoxine or adermine pyridoxol, pyridoxal and pyridoxamine. Pyridoxine was isolated by various study groups in 1938. Its structure was described by Folkers and Kuhn in 1939. Pyridoxal and pyridoxamine were discovered by Snell in 1942. Pyridoxal phosphate and pyridoxamine phosphate are biologically active substances. Intestinal absorption of Bg is dose-dependent and not limited. In alcoholism, a deficiency of vitamin Bg is encountered in 20—30% of cases, whereas the respective percentage is 50—70% in alcoholic cirrhosis. Vitamin Bg is an important coenzyme for transaminases, which transfer amino groups from amino adds to keto acids. In this way, biochemical pathways between the dtiic acid cycle and carbohydrate and amino acid metabolisms are created. (104)... 

F. Vitamin deficiencies that affect amino acid metabolism... 

Besides being fundamental constituents of proteins they are the parent substances from which powerful hormones are derived, for example, adrenaline (epinephrine), noradrenaline (norepinephrine), thyroxine and related substances, 5-hydroxytryptamine (enteramine, serotonin), and the plant hormone indoleacetic acid. Tryptophan is also the precursor of the B vitamin nicotinic acid and hence of part of the important pyridine nucleotides. All three aromatic amino acids are potential precursors of other substances having powerful physiological activity, for example, many of the alkaloids. Errors in the metabolism of the aromatic amino acids in man can give rise to sometimes serious, but fortunately comparatively rare, disorders such as alkaptonuria and phenylketonuria. The numerous metabolic pathways involved in aromatic amino acid metabolism therefore make an important as well as an interesting study. 

A vitamin which, as a coenzyme, plays the greatest role in amino acid metabolism is... 

In this chapter, the metabolism of aromatic amino acids, including histidine, is examined. The aromatic amino acids are dietary essentials, with the exception of tyrosine, which can be formed from phenylalanine. Each of the amino acids has a unique metabolism, including the formation of important compounds other than proteins as neurotransmitters, pigments, and a vitamin. A number of metabolic diseases are also associated with aromatic amino-acid metabolism. An overall view of nitrogen economy and protein metabolism is discussed at the end of the chapter. 

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