Alpha-keto acid

Fig. 8.2 Model for the synthesis of amino acids from alpha-keto acid precursors covalently attached to dinucleotides. The dinucleotide that is capable of catalyzing synthesis of particular amino acids is proposed to contain the first two bases of the codon specifying that amino acid (Copley et al., 2005)...

R. Fernandez-Lafuente, V. Rodriguez, and J.M. Guisan, The coimmobilization of D-amino acid oxidase and catalase enables the quantitative transformation of D-amino acids (D-phenylalanine) into alpha-keto acids (phenylpyruvic acid). Enz. Microb. Technol. 23, 28-33 (1998). 

Mechanism of the Reaction between alpha Keto Acids and alpha Amino Acids. J. org. Chem. 8, 380 (1943). 

El Kaim L, Gageat M, Gaultier L, Grimaud L (2007) New Ugi/Pictet-Spengler multicomponent formation of polycyclic diketopiperazines from isocyanides and alpha-keto acids. Synlett 2007(03) 0500-0502... 

H. Iding, P. Siegert, K. Mesch, M. Pohl, Application of alpha-keto acid decarboxylases in biotransformations. Biochim. Biophys. Acta 1998, 1385, 307-322. 

The photoelectrochemical synthesis of amino acids from simple molecules has also been reported. Low efficiencies were observed in the conversion of mixtures of methane, ammonia and water to several amino acids on platinized TiOz Amino acids and peptides were reported when glucose replaced methane as the carbon source in a parallel experiment Higher quantum efficiencies (20-40%) were observed in the conversion of alpha-keto acids or alpha-hydroxy acids to the corresponding alpha-amino acids Moderate levels of enantiomeric selectivity (optical yields of about 50%) were reported when chiral starting materials were employed. Photoinduced Michael-like reactions were observed when alpha, beta unsaturated acids were used as substrates for the amino acid synthesis... 

Roche, T. E., and Patel, M. E., eds. (1990) Alpha-Keto Acid Dehydrogenase Complexes Organization, Regulation, and Biomedical Ramifications, Vol. 573, New York Academy of Sciences, New York... 

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. 

The process of racemization is important in the survival and growth of living cells and is catalyzed by a group of enzymes called racemases. Alanine racemase. for example, is able to convert n-alanine to DL-alanine if a suitable alpha keto acid is also present. In this reaction the asymmetry of the alpha-carbon atom of alanine is lost as the amino acid is converted to the keto acid and back. This process is analogous to the well-known process of transamination in which racemization seldom occurs. 

Angata T, Varki A (2002) Chemical diversity in the sialic acids and related alpha-keto acids an. evolutionary perspective. Chem Rev 102 439 Arduengo AJ 3rd (1999) Looking for stable carbenes the difficulty in starting anew. Acc Chem Res 32 913... 

Harris RA, KobayashiR, Murakami T, andShimomuraY (2001) Regulation of branched-chain alpha-keto acid dehydrogenase kinase expression in rat livet. Journal of Nutrition 131, 841S-5S. 

TVansaminase—a transferase that transfers an amino group from an amino acid to an alpha-keto acid, especially alpha-ketoglutarate (2-ketoglutaiate). Also called an aminotransferase. 

Branched-chain ketoaciduria (commonly known as Maple Syrup Urine Disease MSUD) is another ailment that may be caused by thiamine deficiency. In MSUD, the oxidative decarboxylation of alpha-keto acids derived from, i.e. valine, isoleucine, and leucine, is blocked due to an inadequate supply of the coenzyme thiamine pyrophosphate (TPP). Clinical symptoms of MSUD include mental and physical retardation. Describe briefly the structure of Riboflavin (Vitamin B-2) and its biochemical role. 

Under these different circumstances amino acids lose their amino groups and the alpha-keto acids so formed may undergo oxidation to CO2 and H2O. In addition, the carbon skeleton of amino acids provides three and four carbon units that can be converted to glucose to be used by body. 

M. C. Fusee, Amino add production from alpha-keto acid by microbiological conversion, German Intent Application DE3427495 Al, 1985. 

A further consequence of thiamine depletion during parenteral nutrition can be severe lactic acidosis (44). Six cases have been described from Japan with associated hypotension, Kussmaul s respiration, and clouding of consciousness, as well as abdominal pain not directly related to the underlying disease. During parenteral nutrition administration there was blockade of oxidative decarboxylation of alpha-keto acids such as pyruvate and alpha-ketoglutarate, resulting in pjruvate accumulation and massive lactate production. None of the patients responded to sodium bicarbonate or other conventional emergency treatments for shock and lactic acidosis. Thiamine replenishment with intravenous doses of 100 mg every 12 hours resolved the lactic acidosis and improved the clinical condition of three patients. 

Lactic acid (2-hydroxypropanoic acid, a-hydroxypropi-onic acid) is the next shortest AHA after glycolic acid. A methyl group (CH3) replaces the terminal hydrogen atom on the alpha carbon (Figure 6.3). It has a of 3.86, which is close to that of glycolic acid. Lactic acid occurs naturally in sour milk. After penetrating the skin, lactic acid is converted automatically and reversibly into pyruvic acid, the alpha-keto acid derivative of lactic acid a keto (=0) function replaces the hydroxy (-OH) function on the alpha carbon. At identical concentrations, lactic acid destroys the epidermis more slowly than glycolic acid. 

It is clear, however, that, as a general rule, and even if some acids have specific properties, most of the hydroxy acids (alpha or beta), carboxylic acids (containing the COOH group), dicarboxylic acids and alpha-keto acids produce the same positive effects on the skin, depending on the concentration, the pH of the solution (Figure 6.4) and how they are applied. 

No data were located regarding the toxicokinetics of hydrazines in humans after inhalation, oral, or dermal exposure to hydrazines. Inhalation, oral, and dermal studies in animals indicate that hydrazines are rapidly absorbed into the blood. Animal studies also indicate that hydrazines readily distribute to tissues w ithout preferential accumulation at any specific site. Hydrazines with a free amino group are able to react with endogenous alpha-keto acids and in so doing produce a variety of adverse health effects. In vivo and in vitro studies indicate that hydrazines are metabolized by several pathways, both enzymatic and nonenzymatic. Free radical and carbonium ion intermediates are produced during the metabolism of hydrazines and may also be involved in adverse health effects produced by exposure to hydrazines. Limited data from animal studies indicate that metabolites of hydrazines are excreted principally in the urine and expired air. Although the data are limited, animal studies appear to indicate that the toxicokinetics of hydrazines may vary among animal species. 

There are at least two distinct mechanisms by which hydrazines produce adverse health effects. Methods for interfering with these mechanisms are discussed below. The first mechanism involves the reaction of hydrazine or 1,1-dimethylhydrazine with endogenous alpha-keto acids such as vitamin Bg (pyridoxine). The formation of hydrazones of pyridoxine is the proposed mechanism by which hydrazine and... 

Many mononuclear nonheme iron oxygenases require a reducing cofactor (pterin or alpha-keto acid) for dioxygen activation.23,128 These enzymes utilize Fe(I V) > Fe (II) reduction by two-electron substrates. A simplified catalytic cycle for 2-keto-glutarate-dependent enzymes is shown in Figure 4.34. Keto-glutarate cofactors assist... 

Alpha amino acids (and aldehydes) synthesis by reaction of an alpha keto acid with another amino acid (Herbst-Engel) or by reaction of a keto acid with ammonia under reducing conditions (Knoop-Oesteriing) (see 1st edition). 

Slla. Seligson, D., and Shapiro, B., Alpha-keto acids in blood and urine studied by paper chromatography. Anal. Chem. 24, 754 (1952). 

T6. Taylor, K. W., and Smith, M. J. H., l,2-diamino-4-nitrobenzene as a reagent for the detection and determination of alpha-keto acids in blood and urine. Analyst 80, 607 (1955). 

Aldridge and Cremer (1958) made a distinction between the biological action of diethyl- and triethyltin compounds, according to which diethyltin compounds also inhibit the functioning of alpha-keto acid oxidase. According to Rose (1971), the toxic and phytotoxic action of triorganotin compounds can be explained by the... 

A. de Kok W. J. H. van Berkel, Lipoamide Dehydrogenase. n Alpha-Keto Acid Dehydrogenase Complexes M. S. Patel,... 

Oxidation of the aldheyde with chromate and pyridine, followed hy ozonolysis with ozone and workup with zinc and acetic acid gives the alpha keto acid 22.20Decarhoxylation with lead tetraacetate gives the alcohol aldehyde 23. 

Citrate is not a good substrate for decarboxylation. Decarboxylation is usually carried out on alpha-keto acids (like pyruvate, above) or alpha-hydroxy acids. Conversion of citrate into an alpha-hydroxy acid involves a two-step process of water removal (dehydration), making a double bond, and readdition (hydration) of the intermediate—aconitate as Figure 10-4 shows. The enzyme responsible for this isomerization is aconitase. 

Water is added across the double bond in the next step, catalyzed by fumarase, to give malic acid, or malate. Finally, malate dehydrogenase removes the two hydrogens from the hydroxyl carbon to regenerate the alpha-keto acid, oxaloacetate ... 

Oxidation at the peptide backbone carbon has been shown to occur from ultraviolet exposure both in wool [38] and in hair [39], producing carbonyl groups (alpha-keto acid/amide) and amide groups. The formation of carbonyl groups is favored in the dry state reaction more than in the wet state. This reaction is similar to the oxidative damage to proteins and mitochondrial decay associated with aging [40]. 

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