Substrate ground state binding energy concentration is realized as transition state stabilization in physiological enzyme catalysis.
Previously published kinetic data on the interactions of seventeen different enzymes with their physiological substrates are re-examined in order to understand the connection between ground state binding energy and transition state stabilization of the enzyme-catalyzed reactions. When the substrate ground state binding energies are normalized by the substrate molar volumes, binding of the substrate to the enzyme active site may be thought of as an energy concentration interaction; that is, binding of the substrate ground state brings in a certain concentration of energy. When kinetic data of the enzyme/substrate interactions are analyzed from this point of view, the following relationships are discovered: 1) smaller substrates possess more binding energy concentrations than do larger substrates with the effect dropping off exponentially, 2) larger enzymes (relative to substrate size) bind both the ground and transition states more tightly than smaller enzymes, and 3) high substrate ground state binding energy concentration is associated with greater reaction transition state stabilization. It is proposed that these observations are inconsistent with the conventional (Haldane) view of enzyme catalysis and are better reconciled with the shifting specificity model for enzyme catalysis.
Department of Chemistry and Physics, Texas Woman's University, Denton, TX 76798, USA. mbritt@twu.edu
Billy Mark
BM
Britt
D002384:Catalysis; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D013816:Thermodynamics
D004798:Enzymes