Models for fluorescence energy transfer between moving donors and acceptors

A number of theoretical models are introduced in which donors and acceptors perform lateral or rotational motion during the time in which fluorescence energy transfer takes place. Each case is reduced to an eigenvalue problem, and for each model calculations are made of observables, such as fluorescence intensities and anisotropies, by employing matrix methods. It is shown that the observables depend on the size of the motional step only if fluorescence energy transfer occurs. This finding indicates that fluorescence energy transfer studies may reveal whether the dynamics of a system (e.g., a protein) is better described in terms of transitions between a number of discrete states or in terms of diffusion equations. Some theoretical tools are offered for analyzing fluorescence energy transfer data without restrictive assumptions for motional averaging regimes or the orientation factor.