Fig. 5. Effects of Twf1 and Cof1 on the fluorescence of actin filaments capped at their barbed ends with gelsolin. Time course of gelsolin-capped actin filament (G-A) fluorescence (40% pyrene labeled) at pH 5.0 after dilution (from 5 µM to 0.25 µM) at time zero in the presence of the indicated proteins. Actin (5 µM) was polymerized in the presence of 25 nM gelsolin. 1 µM CP had no effect on the depolymerization rate, verifying that these filaments were capped efficiently at their barbed ends by gelsolin. A.U., arbitrary units.