Fig. 3.

Steric trapping leads to reversible loss of retinal absorbance. (A) The spectra of the BE-labeled bR-D36C/F230C alone (bR-BE₂ alone, black solid line) and in the presence of saturating concentrations of E44Q/S45A-mSA (∼30–40 μM) (bR-BE₂ + mSA, black dotted line) are shown. To test reversibility, excess free biotin (5 mM) was added to the bR-BE₂ + mSA sample and the spectrum was recorded after a further 1-d incubation (bR-BE₂ + mSA + biotin, red dashed line). (B) Representative forward and reverse binding curves at 0.3 X_SDS. The solid lines in the plot are the fitting results using Eq. 6.