Figure 10. Reaction times, quantum yields and electron-transfer reorganization energies in CPD repair by photolyases.

(A) Top: Reaction times of all elementary steps involved in repair by different photolyases. LT, deactivation lifetime; FET1, forward electron transfer (ET) to adenine; FET2, forward ET directly to substrate; FET3, forward ET from anionic adenine to substrate; BET1b, back ET from anionic adenine to flavin ground state; BET2, back ET from anionic substrate to flavin ground state without repair; SP2, the C6–C6′ bond splitting; ER, electron return after repair. The C5–C5′ bond cleavage is ultrafast and is not shown here. The dashed lines link three sets of competing branching channels responsible for the repair efficiencies. Bottom: Elementary quantum yields (QYs) of three forward ETs and SP2, and the total repair quantum yield Φ_T for each photolyase. The four elementary QYs are calculated as follows: Φ_FET1=<τ_FET1>⁻¹/(<τ_LT⁻¹+<τ_FET1>⁻¹ +<τ_FET2 >⁻¹; Φ_FET2+<τ_FET2>⁻¹/(τ_LT⁻¹+ +<τ_FET1>⁻¹ +<τ_FET2>⁻¹); Φ_FET3=+<τ_FET3>⁻¹/(<τ_FET3>⁻¹+<τ_BET1a>⁻¹+<τ_BET1b>⁻¹); Φ_SP2=<τ_SP2>⁻¹/(<τ_SP2>⁻¹+<τ_BET2>⁻¹). Because the ET between LfH⁻* and adenine interconverts, the overall repair QY is calculated as Φ_T= (Φ_FET2+ Φ_FET1× Φ_FET3)× Φ_SP2×(1+Φ′+Φ′² +Φ′³…), where Φ′=Φ_FET1×[<τ_BET1a>⁻¹/(<τ_FET3>⁻¹+ <τ_BET1a>⁻¹+ <τ_BET1b>⁻¹)]. In all photolyases studied here, Φ′ is less than 0.01 due to a much faster τ_FET3 than τ_BET1a. (B) Two-dimensional (2D) contour plot of the ET dynamics in repair relative to free energy (ΔG⁰) and reorganization energy (λ) for FET2 (filled circle), BET2 (open square) and ER (open diamond). The FET2 is in the Marcus normal region (−ΔG⁰≤ λ) and the ER is in the Marcus inverted region (−ΔG⁰> λ). BET2 is a dissociative ET process and is in the normal region again.