Figure 1.

Absorbance decay of the semiquinones at 450 nm as a function of time after the second of two laser flashes in the presence of various concentrations of ZnSO₄ (a) and CdSO₄ (b). From the decay, the rate constant k_AB⁽²⁾ was determined. Note the slowing of the kinetics with increasing cation concentrations. The pedestal at long times after the laser flash is caused by the absorbance change of the cytochrome c used to reduce the primary donor (see Materials and Methods). Conditions were: 2 μM RCs in 10 mM Tris⋅HCl (pH 7.7), 0.25% lauryl dimethylamine-N-oxide with the concentration of ZnSO₄ or CdSO₄ as indicated in the figure.