Transient-phase energetics of the oxidative deamination of L-glutamate by L-glutamate dehydrogenase and NADP: A reaction with a large negative heat capacity of activation
✍ Scribed by Alan H. Colen; Richard T. Medary; Harvey F. Fisher
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1981
- Tongue
- English
- Weight
- 592 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
A study of the temperature dependence of the initial transient velocities of the oxidative deamination of L‐glutamate by glutamate dehydrogenase and NADP has permitted the determination of the enthalpies, entropies, and heat capacities of the phenomenological parameters for mechanistic steps up to and including the catalytic hydrogen‐transfer step. The most striking feature observed is the extremely large negative heat capacity of activation (−590 ± 150 cal K^−1^ mol^−1^) for the catalytic step itself. Possible sources of such heat capacities are considered, with particular focus on the effects of hidden equilibria among multiple thermodynamic states. Heat‐capacity changes of the sort observed here can be produced by shifts of such dynamic equilibria between multiple forms of the free enzyme induced by the formation of the catalytic transition state.