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An interpretation of fluctuations in enzyme catalysis rate, spectral diffusion, and radiative component of lifetimes in terms of electric field fluctuations

Prakash, Meher K. and Marcus, R. A. (2007) An interpretation of fluctuations in enzyme catalysis rate, spectral diffusion, and radiative component of lifetimes in terms of electric field fluctuations. Proceedings of the National Academy of Sciences of the United States of America, 104 (41). pp. 15982-15987. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:PRApnas07

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Abstract

Time-dependent fluctuations in the catalysis rate ({delta}k(t)) observed in single-enzyme experiments were found in a particular study to have an autocorrelation function decaying on the same time scale as that of spectral diffusion {delta}{omega}0(t). To interpret this similarity, the present analysis focuses on a factor in enzyme catalysis, the local electrostatic interaction energy (E) at the active site and its effect on the activation free energy barrier. We consider the slow fluctuations of the electrostatic interaction energy ({delta}E(t)) as a contributor to {delta}k(t) and relate the latter to {delta}{omega}0(t). The resulting relation between {delta}k(t) and {delta}{omega}0(t) is a dynamic analog of the solvatochromism used in interpreting solvent effects on organic reaction rates. The effect of the postulated {delta}E(t) on fluctuations in the radiative component ({delta}{gamma}Formula(t)) of the fluorescence decay of chromophores in proteins also is examined, and a relation between {delta}{gamma}Formula(t) and {delta}{omega}0(t) is obtained. Experimental tests will determine whether the correlation functions for {delta}k(t), {delta}{omega}0(t), and {delta}{gamma}Formula are indeed similar for any enzyme. Measurements of dielectric dispersion, {varepsilon}({omega}), for the enzyme discussed elsewhere will provide further insight into the correlation function for {delta}E(t). They also will determine whether fluctuations in the nonradiative component {gamma}Formula of the lifetime decay has a different origin, fluctuations in distance for example.


Item Type:Article
Additional Information:© 2007 by The National Academy of Sciences of the USA. Contributed by R. A. Marcus, August 20, 2007 (received for review June 20, 2007). Published online on October 2, 2007, 10.1073/pnas.0707859104. M.K.P. thanks Jau Tang and Yousung Jung for helpful discussions. This work was supported by the National Science Foundation and the Office of Naval Research. Author contributions: M.K.P. and R.A.M. designed research, performed research, analyzed data, and wrote the paper. The authors declare no conflict of interest.
Subject Keywords:fluorescence; single enzyme
Record Number:CaltechAUTHORS:PRApnas07
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:PRApnas07
Alternative URL:http://dx.doi.org/10.1073/pnas.0707859104
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10175
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:16 Apr 2008
Last Modified:14 Nov 2014 19:20

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