Figure 2.

Absorption Spectra and the Photocycle of phy3 LOV2 in the Crystal and in Solution.

(A) Dark-state absorption spectra of phy3 LOV2 in single monoclinic crystals (solid black line) and solution (dashed line) normalized at 411 nm. Actinism of the monitoring light source contributes to a crystal dark-state spectrum containing a small percentage of photoproduct. Decay from the fully bleached spectrum of phy3 LOV2 (gray) is shown at 4 min (blue), 15 min (red), and 40 min (green).

(B) Recovery of the dark state from the photoexcited steady state in solution (open circles) and in the crystal (closed triangles) monitored at 473 nm. A₀ represents the amount of the nonadduct form of LOV2 at time 0, and A_x represents the amount at time x. The linearity of the plots indicates single exponential behavior with decay rates of 0.003 sec⁻¹ in solution and 0.002 sec⁻¹ in the crystal. This kinetic difference corresponds to a difference in the free energy of activation of 0.24 kcal/mol between LOV2 decay in the crystal and in solution.