Figure 8.

Impact of substrate binding on the tryptophan fluorescence of trimeric and monomeric CaiT reconstituted into proteoliposomes. (a) Fluorescence emission spectra of given CaiT variants in proteoliposomes [80 μg mL⁻¹, lipid to protein ratio 20:1 (w/w)] in 100 mM potassium phosphate buffer, pH8, 2 mM β-mercaptoethanol, 5 mM MgCl₂ at 25 °C. All fluorescence data were corrected for a buffer blank and for dilution effects. Shown are the emission spectra of CaiT without substrate (no add.), with 53 mM L-carnitine (+L-Cn) or γ-butyrobetaine (+γ-Bb). (b) Substrate-dependent change of the fluorescence intensity. All other conditions were as described in the legend of Fig. 7.