Key result
Beta-cardiac myosin initiates working stroke within ~200 μs of actin binding, preceding phosphate release.
The working stroke of cardiac myosin occurs prior to phosphate release, providing fundamental insights into the mechanochemistry of cardiac muscle contraction.
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No immediate clinical implications; extends biophysical models of cardiac myosin but leaves open in vivo or therapeutic relevance.
Key steps of cardiac mechanochemistry, including the force-generating working stroke and the release of phosphate (P i ), occur rapidly after myosin-actin attachment. An ultra-high-speed optical trap enabled direct observation of the timing and amplitude of the working stroke, which can occur within <200 μs of actin binding by β-cardiac myosin. The initial actomyosin state can sustain loads of at least 4.5 pN and proceeds directly to the stroke or detaches before releasing ATP hydrolysis products. The rates of these processes depend on the force. The time between binding and stroke is unaffected by 10 mM P i which, along with other findings, indicates the stroke precedes phosphate release. After P i release, P i can rebind enabling reversal of the working stroke. Detecting these rapid events under physiological loads provides definitive indication of the dynamics by which actomyosin converts biochemical energy into mechanical work.
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Woody et al. (2019) studied Cardiac mechanochemistry. 10 mM inorganic phosphate (Pi) and mechanical load vs. 0 mM Pi was evaluated on Timing and amplitude of the working stroke. The working stroke of beta-cardiac myosin occurs within <200 μs of actin binding and precedes phosphate release, with the initial actomyosin state sustaining loads of at least 4.5 pN.
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