Figure 2.

For a Figure360 author presentation of Fig. 2, see the figure legend at https://doi.org/10.1016/j.bpj.2018.06.028#mmc1.

ATPase rates of myosin S1 in the presence of actin and actin-tropomyosin containing troponin with different mutants of troponin T at saturating Ca²⁺. Measurements were made at 25°C and pH 7.0 in solutions containing 1 mM ATP, 3 mM MgCl₂, 34 mM NaCl, 10 mM MOPS, 1 mM dithiothreitol, and 0.1 mM CaCl₂. The concentrations of S1, actin, tropomyosin, and troponin were 0.1, 10, 2.2, and 2.2 μM, respectively. The average rate for wild-type-regulated actin over all experiments was 2.4/s (±0.1). Corrected rate = average of all wild-type experiments^∗ (measured mutant rate/measured wild-type rate). Error bars are the SDs. The solid line shows the rate observed in the absence of troponin and tropomyosin. The dashed line shows the expected behavior if each residue contributed equally to the effect measured.