Figure 5.
Rate of binding of S1 to an excess of pyrene-labeled actin filaments containing tropomyosin and troponin in the absence of ATP at a very low Ca2+ concentration. (A) Averaged time courses of binding to actin-tropomyosin containing wild-type troponin T (curve 1), Δ6 troponin T (curve 2), and Δ14 troponin T (curve 3). Dashed lines are single exponential fits. (B) The observed rate of binding of S1 to actin-tropomyosin containing troponin with different mutants of troponin T is shown. Error bars shown are the SDs for at least five experiments. Conditions are as follows: the same as those in Fig. 4, except that 4 μM pyrene-actin (40% labeled), 0.86 μM tropomyosin, and 1.7 μM troponin were rapidly mixed with 0.4 μM myosin S1. The dashed line shows the expected behavior if each residue contributed equally to the effect measured.