Do anesthetics act by competitive binding to specific receptors? Phase transition of firefly luciferase.
1. Firefly luciferase (FFL) emits a flash of light when mixed with ATP and luciferin in the presence of molecular oxygen. 2. Halothane inhibited FFL at 0.22 mM, while myristic acid inhibited it at 0.68 microM. Under steady-state conditions, myristic acid competed with luciferin. The Lineweaver-Burk plots of anesthetics were nonlinear. 3. The Hill numbers for anesthetics were above 1, while that of myristic acid was below 1 (0.89). Anesthetics interact with FFL cooperatively at multiple sites. The binding site of myristic acid is limited. 4. FFL undergoes a phase transition at 37-40 degrees C. Anesthetics decreased, while myristic acid increased the transition temperature. 5. The contrasting effects of anesthetics and myristic acid are discussed according to Koshland's transition-state model for myristic acid, which involves specific receptors, and Eyring's unfolded-state model for anesthetics, which involves nonspecific conformational change. Fatty acids are receptor-binders and structure-maker of FFL. Anesthetics are non-specific binders and structure-breaker of FFL.
Ueda
I
I
DVA Medical Center, and Department of Anesthesia, University of Utah School of Medicine, Salt Lake City 84148, USA. iueda3032@pol.net
Suzuki
A
A
Kamaya
H
H
D000215:Acylation; D000249:Adenosine Monophosphate / Q000378:metabolism; D000777:Anesthetics / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D002152:Calorimetry, Differential Scanning; D007700:Kinetics; D008156:Luciferases / Q000187:drug effects / Q000378:metabolism*; D019814:Myristic Acid / Q000494:pharmacology; D011485:Protein Binding; D011955:Receptors, Drug / Q000187:drug effects*
D000777:Anesthetics; D011955:Receptors, Drug; D019814:Myristic Acid; D000249:Adenosine Monophosphate; D008156:Luciferases