Stretched exponential decay and correlations from two-state single molecule trajectories

Single molecule techniques offer a unique tool studying the dynamical behaviour of individual molecules, and provide the possibility to construct distributions from individual events rather than from a signal stemming from an ensemble of molecules. Observing the activity of individual lipase molecules for extended periods of time (hours), we get long trajectories, made of "on-state" and "off-state" events. The waiting time probability density function (PDF) of the off-state and the state-correlation function fit stretched exponentials, independent of the substrate concentration in a certain range. The data analysis unravels correlations between off-state events. These findings imply that the fluctuating enzyme model, which involves a spectrum of enzymatic conformations that interconvert on the timescale of the catalytic activity, best describes the observed enzymatic activity. This contribution summarizes some of our recent published results.