Pyridoxamine-pyruvate

In the other, the amino acid is rotated 180° so that the a-hydrogen protrudes behind the plane of the paper. Dunathan studied pyridoxamine pyruvate aminotransferase, an enzyme closely related to PLP-requiring aminotransferases and which catalyzes the transamination of pyridoxal with L-alanine to form pyridox-amine and pyruvate. The same reaction is catalyzed by the apoenzyme of aspartate aminotransferase. In both cases, when the alanine contained 2H in the a position the 2H was transferred stereospecifically into... 

Pyridoxamine pyruvate aminotransferase, stereochemistry of 748 Pyridoxine (vitamin B6) 305s, 738... 

For two transaminases the remaining unknown stereochemical parameter was determined by demonstrating an internal transfer of tritium (dialkyl amino acid transaminase) [28] or deuterium (pyridoxamine-pyruvate transaminase) [27] from the a-position of the substrate L-alanine to C-4 of the cofactor. Internal hydrogen transfer from the a-position of the substrate amino acid to C-4 of PLP has also been demonstrated for two of the abortive transamination reactions, those catalyzed by tryptophan synthase fi2 protein [32] and by aspartate-/8-decarboxylase [31]. In addition, the same phenomenon must occur in alanine transaminase, as deduced from the observation that the enzyme catalyzes exchange of the /8-hydrogens of... 

Inhibits alanine racemase, malate dehydrogenase, pyridoxamine pyruvate transami. 

Inhibits alanine racemase, pyridoxamine-pyruvate aminotransferase. 

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... 

The experiments conclusively prove that the addition of hydrogen to C-4 of the coenzyme occurs at the Si face of the Schiff base. Evidence has already been provided for the syn nature of the tautomeric process in the reaction catalysed by pyridoxamine-pyruvate aminotransferase [107]. If the same precedent is extended to aspartate aminotransferase it then follows that the bond to C that is formed and broken in this case must also be located on the Si face at C-4, in the catalytic complex, as shown in structure 2 (Fig. 53). In other words, the alternative arrangement for syn proton transfer shown in 1 (Fig. 53) is precluded by these experiments. The direction of hydrogen addition to C-4 of the coenzyme in the half-reaction has also been studied using several other L-amino add requiring aminotransferases and in every case the medium hydrogen was shown to add to the Si face at C-4 (Table 5). These experiments have led to the generaUsed view that in B -dependent reactions... 

Subsequent to this work, apoaspartate transaminase was used to assay the stereospecificity of a variety of other transaminases, all of which were shown to involve protonation/deprotonation at the C-4 Si face of the cofactor. These enzymes included pyridoxamine-pyruvate transaminase (EC 2.6.1.30) (26) and a-dialkylamino acid transaminase (27). L-Glutamate decarboxylase (EC 4.1.1.15) catalyzes an abortive transamination reaction when oc-methylglutamate is used as substrate, and this too was shown to occur with protonation at the Si face of C-4 in the intermediate 4d (28) as was the abnormal transamination of D-alanine by serine hydroxymethyltransferase (29). 

Yoshikane, Y., Yokochi, N., Ohnishi, K., Hayashi, H., and Yagi, T., 2006. Molecular cloning, expression and characterization of pyridoxamine-pyruvate aminotransferase. Biochemical Journal. 396 499 507. 

Pyridoxamine pyruvate transaminase, 21 Pyrimidine deaminases, 22 Pyrimidine nucleotides, 90 Pyruvate carboxylase, labeling of, 139 Pyruvate decarboxylase, 50, 51 Pyruvate kinase, 21, 241, 248, 299, 306, 307, 529, 548... 

O. A. Gansow and R. H. Holm (1969), A proton resonance investigation of equi-libra, solute structures, and transamination in the aqueous systems pyridoxamine-pyruvate-zinc(II) and aluminium(III). J. Amer. Chem. Soc. 91, 5984-5993. 

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