Figure 1.

Effect of the D73N mutation on the Ca²⁺ sensitivity and the rate of Ca²⁺ dissociation from reconstituted thin filaments in the absence and presence of cTnI pseudo-phosphorylation. (A) Increases in IAANS fluorescence, which occur as Ca²⁺ binds to the regulatory N-domain of the cTn complex, containing cTnI (□) or cTnI^S22D/S23D (■), reconstituted into thin filaments; and to the regulatory N-domain of the cTn^D73N complex, containing cTnI (◦) or cTnI^S22D/S23D (•), reconstituted into thin filaments. Data represent the mean ± S.E. of at least three titrations fit with logistic sigmoid function. IAANS fluorescence was excited at 330 nm and monitored at 450 nm. (B) Time course of decreases in IAANS fluorescence as Ca²⁺ was removed by excess EGTA from the regulatory N-domain of the cTn complex, containing cTnI or cTnI^S22D/S23D, reconstituted into thin filaments; and from the regulatory N-domain of the cTn^D73N complex, containing cTnI or cTnI^S22D/S23D, reconstituted into thin filaments. The data traces have been normalized and staggered for clarity. Each trace is an average of at least five traces fit with single exponential equation. The IAANS fluorescence was excited at 330 nm and monitored through a 510 nm bandpass filter.