[Arg292----Val] or [Arg292----Leu] mutation enhances the reactivity of Escherichia coli aspartate aminotransferase with aromatic amino acids.
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.
Hayashi
H
H
Department of Medical Chemistry, Osaka Medical College, Japan.
Kuramitsu
S
S
Inoue
Y
Y
Morino
Y
Y
Kagamiyama
H
H
D000595:Amino Acid Sequence; D001120:Arginine; D001219:Aspartate Aminotransferases / Q000235:genetics / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D002384:Catalysis; D002942:Circular Dichroism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D007700:Kinetics; D007930:Leucine; D009154:Mutation; D011487:Protein Conformation; D013053:Spectrophotometry; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014633:Valine
D005971:Glutamates; D001224:Aspartic Acid; D018698:Glutamic Acid; D001120:Arginine; D001219:Aspartate Aminotransferases; D007930:Leucine; D014633:Valine