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

Time-dependent fluctuations in the catalysis rate (δk(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 δω₀(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 (δE(t)) as a contributor to δk(t) and relate the latter to δω₀(t). The resulting relation between δk(t) and δω₀(t) is a dynamic analog of the solvatochromism used in interpreting solvent effects on organic reaction rates. The effect of the postulated δE(t) on fluctuations in the radiative component (δγ[Formula: see text](t)) of the fluorescence decay of chromophores in proteins also is examined, and a relation between δγ[Formula: see text](t) and δω₀(t) is obtained. Experimental tests will determine whether the correlation functions for δk(t), δω₀(t), and δγ[Formula: see text] are indeed similar for any enzyme. Measurements of dielectric dispersion, ε(ω), for the enzyme discussed elsewhere will provide further insight into the correlation function for δE(t). They also will determine whether fluctuations in the nonradiative component γ[Formula: see text] of the lifetime decay has a different origin, fluctuations in distance for example.