Figure 6. KCN titration of (A) P_obs, (B) R and (C) P_adj of the WT and the ΔPSI cells.

P_obs and P_adj of the ΔPSI cells were much more sensitive to KCN than those of the WT cells, whereas R of the ΔPSI cells had the same sensitivity to KCN as that of the WT cells. The I₅₀ values for KCN inhibition were 49 µM for P_obs of the WT cells (Panel A, black closed circles), 1.7 µM for P_obs of the ΔPSI cells (Panel A, red open circles), 46 µM for P_adj of the WT cells (Panel C, black closed circles), 6 µM for P_adj of the ΔPSI cells (Panel C, red open circles) and 30 µM for R of both the WT (Panel B, black closed circles) and ΔPSI (Panel B, red open circles) cells. P_obs, R and P_adj of both the WT and the ΔPSI cells were measured in BG-11 medium in the presence of 5 mM glucose and 10 mM NaHCO₃. The titration curves of the WT cells (black closed circles) are plotted from 2 data sets. The titration curves of the ΔPSI cells (red open circles, for ΔAB, ΔVIII–XI, and ΔPSI/WV strains) are plotted from 5 data sets. Standard errors are indicated. In addition, the KCN sensitivities of both the WT and ΔPSI cells were not affected by the supplemental Cu²⁺ in the growth medium, as the data shown are for cells grown both with and without Cu²⁺ supplement. For each rate, 100% inhibition by KCN means the rate is reduced from the control value (with no KCN) to zero. An inhibition that is greater than 100% in the case of P_obs means that in the presence of KCN, the cells showed net O₂ consumption instead of displaying net O₂ evolution.