FIGURE 6.

Nucleotide release from WT and Asp-11-mutant actins. A, release of ϵ-ATP from monomeric actin was assayed using a stopped flow apparatus. An actin solution dialyzed against G-buffer containing 0.2 mm ϵ-ATP was rapidly mixed with an equal volume of G-buffer containing 1 mm Ca-ATP. The averages of 3, 7, and 7 traces of WT, D11Q, and D11N actins, respectively are shown, and the fine solid line shows fitting with single exponentials. B, exchange of filament-bound ATP with exogenous ϵ-ATP, as assayed by an increase in fluorescence following the addition of 0.1 mm ϵ-ATP to solutions of WT (circles) or D11Q (triangles) actin filaments dialyzed against F-buffer containing 0.1 mm ATP and then treated with Dowex resin to remove free ATP. Solid lines show fitting with single (WT) and double (D11Q) exponentials. AU, arbitrary units.