Figure 4
From: The molecular basis of thin filament activation: from single molecule to muscle
Measurements of the effect of Ca++ on the ATP-dependence of the speed of regulated thin filaments (RTFs) in the in vitro motility assay. (a) Cartoon of the in vitro motility assay (not to scale). (b) The model reproduces the Ca++-dependence of RTF speed as a function of ATP. Note the biphasic behavior at low Ca++ (pCa 7 and 9). Data (circles) are means, error bars show S.E.M. Parameters used in the simulations were N mot = 75, K = 0.217 μM. (c) Single molecule myosin binding frequency (ε), predicted by fitting the model to motility measurements at each Ca++ concentration (hollow circles, error bars show S.D.), agree with our direct, single molecule measurements (data, red squares; error bars, S.D.; best fit, black solid line) and our indirect estimate from fits to the mini-ensemble measurement (dashed line). These individual fits to the in vitro motility data are well-described by equations (1) and (2), with K = 0.217 μM (blue solid line).
