Figure 2.

Fluorescence intensity decays of AEDANS (donor) attached to residue 167 of cTnI in reconstituted cardiac thin filaments. Dotted curves, donor-only sample, solid curve, donor-acceptor sample in which actin was labeled with acceptor DABM at C374. Black, no Ca²⁺ (Mg²⁺ only); red, Ca²⁺ (+ Mg²⁺); Pink, myosin S1 is strongly bound to the filaments and in the absence of Ca²⁺, and blue, myosin is strongly bound to the filaments and in the presence of Ca²⁺. The decays were measured with excitation at 343 nm, and the emission collected at 500 nm. Sample were in 50 mM Mops at pH 7.0, 1mM DTT, 1 mM EGTA, 5 mM MgCl₂, 0.2 M KCl. When Ca²⁺ was present, it was 2 mM CaCl₂. The initial fast decays of these tracings are shown in the inset.