Figure 12.

Leading head conformations and their dependence on nucleotides. (a) Population of straight and sharply bent conformations under different nucleotide conditions. The numbers in (frames) and [molecules] represent those of examined images and molecules, respectively. (b) Average lifetime ⟨τ_ST⟩ during which the leading head assumes the straight conformation in various ADP concentrations (the number of events used to obtain the average is shown in ⟨events⟩). The error bar indicates standard error. The line curve indicates the best fit result obtained by analyzing the data using the following equation: ⟨τ_st⟩ = n_NF/k_S–B + n_ADP/k_–, where k_S–B represents the spontaneous transition rate of the nucleotide-free leading head from the straight conformation to the sharply bent conformation, k_– represents the ADP dissociation rate constant for the leading head, and n_NF and n_ADP are, respectively, the fractions of nucleotide-free and ADP-bound leading head under a given ADP concentration, which can be calculated using the ADP dissociation constant K_d of 0.075 μM estimated from the data shown in (a).