FIGURE 3.

Accessibility of mBBr labeled bovine rhodopsin and parapinopsin mutants for fluorescence quenching agent KI. Top panels, A–H, Stern-Volmer plots of bovine rhodopsin mutants 227B₁ (A), 244B₁ (B), 250B₁ (C), and 251B₁ (D) and parapinopsin mutants 227B₁ (E), 244B₁ (F), 250B₁ (G), and 251B₁ (H) are shown. Stern-Volmer plots report the ratio of fluorescence intensity in the absence (Fo) and presence (Fi) of quencher as a function of quencher concentration. All of the mutants were labeled with mBBr. The closed and open circles indicated Fo/Fi values in the dark state and after photoactivation, respectively. Bottom panels, I–N, bimolecular quenching constant (kq) of respective mutants. The kq value was determined as the ratio of the slop of Stern-Volmer plot Ksv over the fluorescent lifetime τ (kq = Ksv/τ) (see supplemental Table S1). Black and white bars indicate kq values before (D) and after (L) photoactivation, respectively. Data are presented as the means ± S.E. of at least three separate experiments.