PMID:12966078
| Citation |
Islam, MM, Hayashi, H and Kagamiyama, H (2003) Reaction of aspartate aminotransferase with C5-dicarboxylic acids: comparison with the reaction with C4-dicarboxylic acids. J. Biochem. 134:277-85 |
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| Abstract |
The reaction of Escherichia coli aspartate aminotransferase (AspAT) with glutamate and other C5-dicarboxylates was analyzed in order to compare its mechanism of action toward C5 substrates with that toward C4 substrates, which had been extensively characterized. The association of the amino-group protonated and unprotonated forms of glutamate (SH(+) and S, respectively) with the Schiff-base protonated and unprotonated forms of the enzyme (E(L)H(+) and E(L), respectively) yields at least three forms of the Michaelis complex, whereas in the case of aspartate, only two species of this complex exist, E(L).SH(+) and E(L)H(+).S. The reaction of AspAT with 2-methylglutamate can be explained only when we consider all the protonation states of the Michaelis complex. Based on the previous crystallographic studies [Miyahara et al. (1994) J. Biochem. 116, 1001-1012], we consider that glutamate binds to the open form of AspAT and takes an extended conformation in the Michaelis complex, with the alpha-amino group of glutamate oriented in the opposite direction to the Schiff base. This is in contrast to the Michaelis complex of aspartate, in which a strong interaction of the alpha-amino group of aspartate and the Schiff base excludes the presence of the species E(L)H(+).SH(+). It is concluded that AspAT recognizes the two types of dicarboxylates with different chain lengths by changing the gross conformation of the enzyme protein. |
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| Keywords |
Aspartate Aminotransferases/chemistry; Aspartate Aminotransferases/metabolism; Aspartic Acid/chemistry; Aspartic Acid/metabolism; Escherichia coli/enzymology; Glutamic Acid/chemistry; Glutamic Acid/metabolism; Hydrogen-Ion Concentration; Kinetics; Models, Molecular; Protein Binding; Spectrophotometry/methods; Substrate Specificity; Thermodynamics |
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