Key result
The association constant of S-1 with regulated actin was similar in the absence of Ca2+ (1.3 X 10^4 M-1) and presence of Ca2+ (2.3 X 10^4 M-1), suggesting troponin-tropomyosin does not block binding.
Population
Vertebrate skeletal muscle actin-troponin-tropomyosin complex and myosin subfragment 1 (S-1)
Comparison
Absence of Ca2+ vs Presence of Ca2+
Design
Preclinical
Authors
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Challenges steric blocking model of thin filament regulation; leaves open precise mechanism of Pi release inhibition in cardiac muscle.
Absolute Event Rate: 13000% vs 23000%
The troponin-tropomyosin complex does not inhibit actin-activated ATPase activity by preventing myosin binding to actin, but likely by blocking the release of Pi from the acto-S-1-ADP-Pi complex.
Chalovich et al. (1981) studied this question. Absence of Ca2+ vs. Presence of Ca2+ was evaluated on Association constant of myosin subfragment 1 (S-1) with the actin-troponin-tropomyosin complex. The association constant of S-1 with regulated actin was similar in the absence of Ca2+ (1.3 X 10^4 M-1) and presence of Ca2+ (2.3 X 10^4 M-1), suggesting troponin-tropomyosin does not block binding.
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