Figure 4.

The 9,11-bridged retinal acts to rescue the long-lived O intermediate in the Leu-93 → Thr mutant. (A) Transient changes in absorbance of the Leu-93 → Thr mutant (with native retinal) showing the kinetics of the M (measured at 410 nm) and O (measured at 625 nm) intermediates. (B) Same as in A except native retinal was replaced by the 9,11-bridged retinal. Transient absorbance changes at 410 nm are due to the formation and decay of the M intermediate, but unlike with native retinal (A) no absorbance changes that can be assigned to the O intermediate are observed at 625 nm.