Figure 7.

Time-resolved spectroscopy of the reverse photocycle. A, time trace of the absorption changes at selected wavelengths from ^15EPo to ^15ZPb conversion. Absorption changes were monitored for the samples in the buffer containing 100% H₂O (black) or 100% D₂O (blue). These traces were fitted with three exponentials (solid line). Time constants τ₁, τ₂, and τ₃ are shown as vertical dotted lines. B, absorption spectra of three intermediates P₆₁₀ (black), P₅₃₀-I (red), and P₅₃₀-II (blue) and the final product (green), which was calculated by the subtraction of absorption changes from the initial ^15EPo spectrum (gray, solid line). The good agreement between the final product (green) and ^15ZPb spectra (gray, dashed line) demonstrated that the final product corresponds to ^15ZPb. C, effect of the H₂O/D₂O ratio on the time constants τ₁, τ₂, and τ₃.