Observation of a Power-Law Memory Kernel for Fluctuations within a Single Protein Molecule

The fluctuation of the distance between a fluorescein-tyrosine pair within a single protein complex was directly monitored in real time by photoinduced electron transfer and found to be a stationary, time-reversible, and non-Markovian Gaussian process. Within the generalized Langevin equation formalism, we experimentally determine the memory kernel K(t), which is proportional to the autocorrelation function of the random fluctuating force. K(t) is a power-law decay, t^-0.51±0.07 in a broad range of time scales (10^-3 10 s). Such a long-time memory effect could have implications for protein functions.