Probing the Role of Dynamics in Hydride Transfer Catalyzed by Lactate Dehydrogenase
Nickolay Zhadin 1, Miriam Gulotta 1 and Robert Callender 1*
1 Albert Einstein College of Medicine
* To whom correspondence should be addressed. E-mail: call{at}aecom.yu.edu.
Submitted on February 27, 2008
Revised on April 16, 2008
Accepted on 25 April 2008
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Abstract |
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TThe dynamical nature of the interconversion of pyruvate to lactate as catalyzed by lactate dehydrogenase (LDH) is characterized by laser induced temperature jump relaxation spectroscopy with a resolution of 20 ns. An equilibrium system of LDH·NADH plus pyruvate and LDH·NAD+ plus lactate is perturbed by a sudden T-jump, and the relaxation of the system is monitored by NADH emission and absorption changes. The substrate binding pathway is observed to be similar, although not identical, to previous work on substrate mimics: an encounter complex is formed between LDH·NADH and pyruvate, which collapses to the active Michaelis complex. The previously unresolved hydride transfer event is characterized and separated from other unimolecular isomerizations of the protein important for the catalytic mechanism, like loop closure, a slower step, and faster events on the nanosecond-microsecond time scales whose structural basis is not understood. The results of this study show that this approach can be applied quite generally to enzyme systems and report on the dynamical nature of proteins over a very wide time range.
Key Words:
enzyme dynamics, kinetics, temperature jump
