Probability of binding of myosin heads to the non-regulated or regulated filaments in rigor conditions or in the presence of ATP-γ-S. (a–c) HS-AFM images of HMM molecules bound between two actin filaments in the presence of ATP-γ-S (a), HMM molecules bound between two actin filaments in the absence of Ca²⁺ and ATP (b) and HMM molecules bound between two cardiac thin filaments in the absence of Ca²⁺ and ATP (c). Scale bars, 30 nm. (d–f) Probabilities of binding of the HMM heads in the F-actin–HMM complex in the presence of ATP-γ-S (d, 1,145 events), in the absence of Ca²⁺ and ATP (e, 1,408 events) and in the cTFs–HMM complex in the absence of Ca²⁺ and ATP (f, 663 events). Individual data points are shown for each HMM molecules (M1–M4) as mean values ± 95% CI, n = 3. (g–i) Corresponding fractional occupancies of the binding sites by HMM heads for the conditions shown in d–f.