Arg292----Val] or [Arg292----Leu] mutation enhances the reactivity of Escherichia coli aspartate aminotransferase with aromatic amino acids |
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Authors: | H Hayashi S Kuramitsu Y Inoue Y Morino H Kagamiyama |
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Affiliation: | Department of Medical Chemistry, Osaka Medical College, Japan. |
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Abstract: | Arg292 of E. coli aspartate aminotransferase was substituted with valine or leucine by site-directed mutagenesis. In comparison with the wild-type enzyme, either of the mutant enzymes showed a decrease by over 5 orders of magnitude of kcat/km values for aspartate and glutamate. This supports the contention that Arg292 is important for determining the specificity of this enzyme for dicarboxylic substrates. In contrast, mutant enzymes displayed a 5- to 10-fold increase in kcat/Km values for aromatic amino acids as substrates. Thus, introduction of an uncharged, hydrophobic side chain into position 292 leads to a striking alteration in substrate specificity of this enzyme, thereby improving catalytic efficiency toward aromatic amino acids. |
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