Figure 5.

(A) ET from Co(terpy)₂²⁺ to oxidized WT*K79H at pH 5 as a function of time monitored by absorbance at 550 nm, A₅₅₀. The time axis is logarithmic. Data are shown at 6 different Co(terpy)₂²⁺ concentrations. The absolute magnitudes of A₅₅₀ have been adjusted so that the data at different Co(terpy)₂²⁺ concentrations can be compared readily. For data collected with a 10 mm pathlength, the following adjustments were made: 0.52 mM, no adjustment to A₅₅₀; 1.02 mM, observed A₅₅₀ – 0.27; 2.04 mM, observed A₅₅₀ – 0.8. For data collected with a 2 mm pathlength, the following adjustments were made: 3.18 mM, observed A₅₅₀ – 0.06; 4.28 mM, observed A₅₅₀ – 0.19; 5.68 mM, observed A₅₅₀ – 0.30. The solid black curves are fits of each data set to a triple exponential rise to maximum equation. (B) Dependence of k_obs,1 on Co(terpy)₂²⁺ concentration obtained from fits to the data in panel A. The slope of this line yields k_ET = 6.8 ± 0.1. Similar plots at pH values from 5.5 to 8 are given in Figure S1 of the Supporting Information. The k_ET values from fits to a linear equation are collected in Table 1.