Effects of Tm-FHC mutants on actin-S1 ATPase activity. Data obtained by continuously monitoring Pi liberation (see Methods). A. Effects of Tm and Tn +/− Ca2+. ATPase was monitored during successive additions of S1, actin, Tm, Tn, EGTA to a solution containing, 0.1mM CaCl2, 15 mM NaCl, 3 mM MgCl2, 1 mM DTT and 1 mM ATP in buffer (10 mM HEPES, pH 7.5). Data were normalized to actin-S1 activity after subtracting the background S1 ATPase. B. ATPase vs. [Ca2+]. CaCl2 was titrated into the reconstituted actinTmTn thin filament in buffer containing 1mM
EGTA and 1 mM NTA. Data were normalized to the high [Ca2+] values fitted to the Hill equation. Background S1 alone ATPase was subtracted.