title: Histidyl-tRNA synthetase from Salmonella typhimurium: specificity in the binding of histidine analogues.
abstract: The topography of the active site of histidyl-tRNA synthetase has been investigated by determining Ki values for a variety of structural analogues of histidine, using the ATP-PPi exchange and tRNA aminoacylation reactions. Using these kinetic constants it has been possible to have a measure of the relative binding affinity of the enzyme for the histidine analogues. The following conclusions have been drawn: (a) the enzyme is stereospecific in the formation of aminoacyl-tRNA complexes, since the D-isomer of histidine does not influence the two reactions; (b) the carboxyl group is not required for binding; (c) bulky derivatives of the carboxyl group prevent the molecules from binding to the enzyme; (d) the amino group permits a good binding affinity; (e) the length of the ring side chain plays a very important role as point of attachment to the enzyme; (f) the kinds of heteroatoms on the ring determine the inhibitory properties of the analogues.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001665:Binding Sites; D006639:Histidine / Q000031:analogs & derivatives*; D006643:Histidine-tRNA Ligase / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000201:enzymology*; D013329:Structure-Activity Relationship
chemical_list: D006639:Histidine; D000255:Adenosine Triphosphate; D000604:Amino Acyl-tRNA Synthetases; D006643:Histidine-tRNA Ligase