Figure 1.

Absorbance decay of the semiquinones at 450 nm as a function of time after the second laser flash in the presence of 10 μM, 100 μM, or 1000 μM CdSO₄ in the DN(M17) [Asp-M17 → Asn] RCs. From the decay, the rate constant k_AB⁽²⁾ was determined. Note the slowing of the kinetics with increasing CdSO₄ concentrations. A similar behavior is observed in the DN(L210) [Asp-L210 → Asn] RCs (data not shown). This is in contrast to the behavior of native RCs, where no change in the kinetics is observed above CdSO₄ concentrations of 10 μM. The pedestal at long times is due to the absorbance change of Cyt c used to reduce the primary donor. Conditions: 2 μM RCs in TL buffer, pH 7.7; concentrations of CdSO₄ as indicated.