k_1 ATP th_1 Force d kT k_2 th_2 Force d kT k_3 ATP th_3 Force d kT k_4 th_4 Force d kT k_1 ATP th_1 Force d kT k_2 th_2 Force d kT k_3 ATP th_3 Force d kT k_4 th_4 Force d kT d fwd_step1 fwd_step2 2 back_step1 back_step2 2 S_tot time d Fw_1st_step Fw_2nd_step 2 Bw_1st_step Bw_2nd_step 2 S_tot S0 S1 k_3 S0 ATP th_3 Force d kT k_4 S1 th_4 Force d kT k_1 S0 ATP th_1 Force d kT k_2 S1 th_2 Force d kT