Conformational changes during enzyme catalysis: role of water in the transition state.
The entropy of activation for the synthesis of Ile-tRNA is high and positive. The only likely source of a high delta S is the loss of structured water as the enzyme . substrate complex moves toward the transition state. This requires a change in the orientation or nature of water-organizing residues in the interface between the enzyme . substrate complex and the water. Such changes, which may be some distance from the "active site," are coupled to the active site in such a way that the increased entropy and decreased free energy of the water--enzyme interface is available at the "active site" to reduce the free energy of activation. The effects of Hofmeister anions on KmS and KcatS are consistent with the entropy data.
D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D000838:Anions / Q000494:pharmacology; D007532:Isoleucine / Q000378:metabolism*; D007533:Isoleucine-tRNA Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D011487:Protein Conformation; D012346:RNA, Transfer, Amino Acyl / Q000096:biosynthesis*; D013816:Thermodynamics; D046249:Transfer RNA Aminoacylation; D014867:Water / Q000378:metabolism*
D000838:Anions; D012346:RNA, Transfer, Amino Acyl; D007532:Isoleucine; D014867:Water; D000604:Amino Acyl-tRNA Synthetases; D007533:Isoleucine-tRNA Ligase