Aminoacyl-tRNA synthetases from Bacillus stearothermophilus. Asymmetry of substrate binding to tyrosyl-tRNA synthetase.
The interaction of L-tyrosine, L-tyrosyladenylate and tRNA-Tyr with tyrosyl-tRNA synthetase from Bacillus stearothermophilus was studied by equilibrium dialysis, gel filtration and fluorescence spectroscopy. The enzyme, which consists of two identical subunits (mol. wt 2 x 44000), binds only a single molecule of L-tyrosine per dimer with a K-d of 2 x 10-5 M at pH 7.8 and 23 degrees C. The tyrosyl-tRNA synthetase--tyrosyladenylate complex which was isolated by gel filtration also has one adenylate bound per dimeric enzyme molecule. In contrast, two tRNA-Tyr molecules bind per enzyme dimer, but the two binding sites are not equivalent having K-d values of 2 x 10-7 M and 1.3 x 10-6 M respectively at pH 6.5 and 25 degrees C. Since crystallographic analysis of the free enzyme [2] shows that the monomer is the asymmetric unit, the data indicate that substrate binding induces asymmetry in the enzyme.
D000249:Adenosine Monophosphate; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001665:Binding Sites; D003956:Dialysis; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D046249:Transfer RNA Aminoacylation; D014443:Tyrosine; D014448:Tyrosine-tRNA Ligase / Q000378:metabolism*
D046911:Macromolecular Substances; D000249:Adenosine Monophosphate; D014443:Tyrosine; D000604:Amino Acyl-tRNA Synthetases; D014448:Tyrosine-tRNA Ligase