Fig. 4
Model simulation of the mechanical output of the machine. a Kinetic scheme, with three states of the myosin head (blue): D, detached; A1 and A2, attached to one monomer of the actin filament (brown). The scheme includes the possibility that during shortening the attached head in the A2 state slips to the next actin monomer farther from the centre of the sarcomere (red). The probability of a second slipping to the pink monomer is limited to 1/10 of that of the first slipping. Details on the strain dependence of the rate functions and how they are constrained by fitting skeletal muscle performance are in Supplementary Fig. 6. The corresponding equations are listed in Supplementary Table 1. The effect of trap compliance on the nanomachine performance is detailed in Supplementary Fig. 7. b F–V relation calculated for a number of available heads, N = 16 (continuous line) and experimental relation from Fig. 2e (open circles and dashed line). c Corresponding P–F relations. d Dependence on N of the three parameters featuring the machine performance, as indicated in the ordinate of each plot. The dashed lines are the respective experimental values. e Relation between number of attached heads (Na) and force relative to F0 calculated with the model for N = 16 (continuous line) and 32 (dotted line)
