title: Conformational changes in complex macromolecules studied by single donor-acceptor pair fluorescence.
abstract: A single donor-acceptor (D-A) pair with a fluctuating FRET rate F is studied theoretically in the frame of a "two-state model" in which the FRET rate F fluctuates taking two values, F1 and F2, with average rates B for the forward and b for the backward transitions. Theoretical expressions are derived for the autocorrelation function g((2))(DA)(τ) and for the Mandel parameter Q(D,A)(τ) allowing for background emission. Fluctuating intensities ID,A(t) and FRET efficiency E(t) = IA(t)/[IA(t) + ID(t)] are calculated with the help of the Monte Carlo technique. The probability w(D,A)(N)(T) of finding N photons in a time interval T, and the distribution of the FRET efficiency P(E) are found by statistical treating of the fluctuating intensities ID,A(t). The shape of the distribution w(D,A)(N)(T) enables one to find the values of the parameters: F1, F2, and b/B. The influence of the background light on g((2))(DA)(τ), Q(D,A)(τ) and w(D,A)(N)(T) is studied. It is shown how the background light influences the ratio b/B found from the analysis of w(D,A)(N)(T) and P(E).
authors.affiliation: Molecular Spectroscopy Department, Institute for Spectroscopy, Russian Academy of Sciences, Moscow, Troitsk 142190, Russia. osadko@isan.troitsk.ru.
authors.forename: Igor S
authors.initials: IS
authors.lastname: Osad'ko
mesh_terms: D004247:DNA / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer; D008027:Light; D008962:Models, Theoretical; D009010:Monte Carlo Method; D017785:Photons; D011506:Proteins / Q000737:chemistry
chemical_list: D011506:Proteins; D004247:DNA