FIGURE 6.

Actin-activated ATPase activity in the absence of Ca²⁺ with increasing concentrations of NEM-S1. (A) The rates of mutant 45 (solid bars) and WT (shaded bars); (B) mutant 43/45 (solid bars) and WT (shaded bars); and (C) mutant 43/45/144 (solid bars) and WT (shaded bars). (D) The ratio of mean ATPase rates with (mutant 45)/(WT), (mutant 43/45)/(WT), and (mutant 43/45/144)/(WT) at different NEM-S1 concentrations (0, 0.5, 1, 4 μM). All rates were corrected for the ATPase rate of S1 and NEM-S1. Data for panels A, B, and C are presented as mean values ± SD with the number of trials in parentheses. Conditions are: 25°C, pH 7, 0.1 or 0.2 μM S1, 10 μM actin, 1 mM ATP, 10 mM MOPS, 3 mM MgCl₂, 33 mM NaCl, 1 mM dithiothreitol, 1 mM EGTA. Actin concentration was increased by an equal amount as the NEM-S1 added to maintain the same number of binding sites. Actin/tropomyosin/troponin was 7:1.5:1.5.