Figure 5
From: The molecular basis of thin filament activation: from single molecule to muscle
Strong-binding activation is necessary and sufficient to fit fiber data with the model. If strong-binding activation can be neglected, then the isometric force developed by a muscle fiber, which is proportional to the number of strongly bound myosin, should be described by the same curve as single molecule data. The response of a single myosin molecule to calcium (thin black line, pCa50 = 5.96, α = 1.4 ± 0.3, mean plus/minus SD) is inconsistent with measurements of isometric force as a function of Ca++ 18 (filled circles, error bars show SEM). Even when the pCa50 of the single molecule curve is adjusted to match the measurements (dashed black line), the curve is not steep enough to fit the data. When strong-binding activation is included in the model (hollow circles, error bars show SD), simulation results are consistent with the measurements since a Hill fit to the model (heavy blue line, pCa50 = 6.81 ± 0.03, α = 1.71 ± 0.19, mean plus/minus SD) also fits the measurements. ATP concentration 4000 μM.
