Supplementary Figure 6: Computation of the spectral overlap integral J.

Computation of the spectral overlap integral J for the FRET pair Atto550-Atto647N in sample 1. Normalized donor fluorescence and acceptor absorption spectra normalized to the maximum (left scale). Spectral overlap density j(λ)(right scale) to compute the spectral overlap integral J[cm⁻¹M⁻¹nm⁴]with \(J = \mathop {\smallint }\limits_0^\infty {\mathrm{j}}\left( \lambda \right){\mathrm{d}}\lambda\) and \(j(\lambda ) = \bar F_D\left( \lambda \right)\varepsilon _A\left( \lambda \right)\lambda ^4\). The extinction coefficient ε_A of Atto647N was assumed to be 150000M⁻¹cm⁻¹ at the maximum as provided by the manufacturer. The donor fluorescence and the acceptor absorption spectra were recorded in two laboratories in at least three independent experiments. Spectra with a flat baseline were selected. The computation was performed once.