Amino acid transamination

Figure 29.15 Mechanism of steps 2-4 of amino acid transamination, the conversion of a PLP-amino acid imine to PMP and an a-keto acid.

Macko, S.A., Estep, M.L.E., Engel, M.H. and Hare, RE. 1986 Kinetic fractionation of stable nitrogen isotopes during amino acid transamination. Geochimica et Cosmochimica Acta 50 2143-2146. 

Essential amino acid Transamination Reductive amination... 

Products of Amino Acid Transamination Name and draw the structure of the a-keto acid resulting when each of the following amino acids undergoes transamination with a-ketoglutarate (a) aspartate, (b) glutamate, (c) alanine, (d) phenylalanine. 

Amino acid Transamination product Decarboxylation product Notes... 

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 ... 

Among the various enzymes capable of producing optically-active amino acids, transamination reactions, catalyzed by enzymes known as aminotransferases or transaminases, have broad potential for the synthesis of a wide variety of enantio-merically pure (R)- and (S)-compounds containing amine groups. Indeed, various examples of the use of aminotransferases for the production of d- and L-amino acids, both naturally-occurring and non-natural, have been published17 151. In addition, certain aminotransferases have been found to act on amines, and methods for the production of enantiomerically pure amines by transamination have been described116-211. This method allows for yields of up to 100% whereas routes based on hydrolases require external racemization to reach such yield levels. In this section we will focus on the application of aminotransferases. 

L13. Lin, E. C. C., Pitt, B. M., Given, M., and Knox, W. E., The assay of aromatic amino acid transaminations and keto acid oxidation by the enol borate-tauto-merase method. ]. Biol. Chem. 233, 668-673 (1958). 

The general arguments about the antiquity of cofactors apply to PLP. The nonenzymatic synthesis of pyridoxal under prebiotic conditions is considered possible, whereas the presence of a 5 phosphate group could hint to an ancestral attachment of the cofactor to RNA molecules. " Furthermore, there are specific grounds to assume that PLP arrived on the evolutionary scene before the emergence of proteins. In fact, in current metabolism, PLP-dependent enzymes play a central role in the synthesis and interconversion of amino acids, and thus they are closely related to protein biosynthesis. In an early phase of biotic evolution, free PLP could have played many of the roles now fulfilled by PLP-dependent enzymes, since the cofactor by itself can catalyze (albeit at a low rate) reactions such as amino acid transaminations, racemizations, decarboxylations, and eliminations. " This suggests that the appearance of PLP may have preceded (and somehow eased) the transition from primitive RNA-based life forms to more modern organisms dependent on proteins. 

See also Enzymes of the citric acid cycle, Figure 14.3, Table 14.1, Citric Acid Cycle Intermediates in Amino Acid Metabolism, Glutamate as a Precursor of Other Amino Acids, Transamination in Amino Acid Metabolism... 

See also Glutamate as a Precursor to Other Amino Acids, Transamination in Amino Acid... 

What are some common features in amino acid biosynthesis In the anabolism of amino acids, transamination reactions play an important role. Glutamate and glutamine are frequently the amino-group donors. The enzymes that catalyze transamination reactions frequently require pyridoxal phosphate as a coenzyme. One-carbon transfers also operate in the anabolism of amino acids. Carriers are required for the one-carbon groups transferred. Tetrahydrofolate is a carrier of methylene and formyl groups, and S-adenosylmethionine is a carrier of methyl groups. 

Transamination is effected by enzymes specific to particular amino acids. Transamination between aspartate and a-keto-glutarate illustrated in Fig. 22-6 results in the production of oxaloacetate and glutamate. 

Fig. 3.3 Krebs cycle in hypoglycemia. This fundamental metabolic pathway is altered during hypoglycemic coma. The Krebs cycle continues to turn, however short the glucose supply from Embden—Myerhof glycolysis is, due to a short circuit of metabolites across the circle by amino acid transamination...

This coenzyme occupies a unique position, in that it is involved in at least four types of reactions which all appear to be quite different. These are the decarboxylation of amino acids, transamination, and the synthesis and cleavage of tryptophan. However, all these reactions, as we shall see, have one thing in common they involve an a-amino acid and are concerned with either the amino group or the carbon atom adjacent to the amino group. 

In the tissues, vitamin Be occurs predominantly as the phosphate of pyridoxal or pyridoxamine, especially the former, except in the liver. Pyri-doxal phosphate functions as a coenzyme in four types of reactions decarboxylation of amino acids, transamination, and the synthesis and cleavage of tryptophan (Chapter 19). This coenzyme is necessary for the deamination of amino acids and for the formation of urea nitrogen. It appears to be essential for the conversion of tryptophan to the pyridine coenzymes. Pyridoxine may be related to fatty acid metabolism and seems to be necessary for normal adrenal cortical function. ... 

Figure 9.9 Transdeamination of amino acids — transamination linked to oxidative deamination.

Transamination. It is involved in shifting an amino group (NHj) from a donor amino acid to an acceptor acid to form another amino acid. This reaction is important in the formation of nonessential amino acids. Transamination is illustrated in Fig. V-31. 

Rudman and Meister IJ ) first showed the presence of a transaminase in cell-free extracts of E. colt that catalyze transamination reactions between glutamate and isoleucine, valine, leucine, norleucine, and norvaline. These monocarboxylic amino acids transaminated with each other as well as with glutamine. Preparations of an E. cdi mutant which did not respond to a-keto- 8-methylvalerate was unable to transaminate isoleucine or valine. The transaminase responsible for activity with the branched-chain amino acids was separated from other transaminases and considerably purified by standard methods of protein purification. It was shown to... 

Amino acid degradation is important for the synthesis of volatile compounds and the transamination of some amino acids methionine, branched-chain, and aromatic amino acids. Transamination is the main degradation pathway that leads to the formation of a-keto acids, which are then degraded into various aromatic compounds. The conversion of amino acids to keto- and hydroxyl acids is initiated by lactobacilli, and Lactococcus strains further convert these products to carboxylic acid. This cooperation between LAB and non-starter LAB can enhance cheese flavor. 

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