Convex Arrhenius plots and their interpretation.
This paper draws attention to selected experiments on enzyme-catalyzed reactions that show convex Arrhenius plots, which are very rare, and points out that Tolman's interpretation of the activation energy places a fundamental model-independent constraint on any detailed explanation of these reactions. The analysis presented here shows that in such systems, the rate coefficient as a function of energy is not just increasing more slowly than expected, it is actually decreasing. This interpretation of the data provides a constraint on proposed microscopic models, i.e., it requires that any successful model of a reaction with a convex Arrhenius plot should be consistent with the microcanonical rate coefficient being a decreasing function of energy. The implications and limitations of this analysis to interpreting enzyme mechanisms are discussed. This model-independent conclusion has broad applicability to all fields of kinetics, and we also draw attention to an analogy with diffusion in metastable fluids and glasses.
Truhlar
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D
Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455-0431, USA. truhlar@umn.edu
Kohen
A
A
D000426:Alcohol Dehydrogenase / Q000737:chemistry*; D004795:Enzyme Stability; D005898:Glass; D007700:Kinetics; D011336:Probability; D013816:Thermodynamics
D000426:Alcohol Dehydrogenase