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The catalytic activity of an enzyme is well described by the Michaelis- Menten(MM)
mechanism. Recent advances in single-molecule fluorescence spectroscopy reveal the presence
of conformational fluctuations, at time scale longer than or comparable to the catalytic reaction
step, that leads to temporal fluctuations in the catalytic rate resulting in dynamic disorder. One
such statistical measure of temporal fluctuation is the dimensionless ratio of the variance and the
square of the mean known as the randomness parameter. In the presence of slow conformational
fluctuations, the randomness parameter is greater than unity indicating the presence of dynamic
disorder in the reaction pathway. In our work we employ theoretical approaches such as the first
passage time distribution formalism and the chemical master equation analysis to model the
kinetics of a single fluctuating enzyme. We obtain exact expressions of the mean turnover time
and randomness parameter. Our results show that fluctuations of the enzyme and enzyme–
substrate conformers can lead to a variation of the randomness parameter with substrate
concentration and also act as a source of dynamic cooperativity in single enzymes. Recent
single-enzyme turnover experiments also provide evidence that the measure of the randomness
parameter generate new fundamental insights on the possible mechanisms underlying such
catalytic reactions. We use our theoretical approaches to study different single enzyme catalyzed
reactions involving inhibitors, multiple substrates and show that the measurement of randomness
parameter can qualitatively distinguish different mechanistic pathways involved in such reactions.
S. Chaudhury, J. Cao and N. A. Sinitsyn, J. Phys. Chem. B 2013, 117, 503– 509
S. Chaudhury, J. Phys. Chem. B, 2014, 118, 10405–10412
D. Singh and S. Chaudhury, J. Chem. Phys., 2017, 146, 145103
D. Singh and S. Chaudhury, ChemBioChem, 2018, 19,842 –850 |