Figure 8.

Predicted gamma distributed PDF_tatt(t) for the two myosin isoforms under varying MgATP conditions at 37°C. (a) The parameter values estimated for the α-MyHC demonstrate an increasing shape parameter and prolonged t_att as MgATP was reduced. The resulting PDF_tatt(t) looks more Gaussian in shape rather than exponential as MgATP was reduced. This would be consistent with a longer rigor state prior to MgATP binding and detachment of the myosin crossbridge. (b) The distributions for β-MyHC represent longer t_att compared to α-MyHC. Again, a longer rigor state would arise with lower MgATP. (c, d) In the α-MyHC at 5 mM MgATP, the release of P_i, release of ADP, and binding of ATP occur in relatively quick succession. The time periods that represent the P_i and ADP states, however, would not be affected by MgATP availability. With the reduction in MgATP concentration, the rigor state would be prolonged as detected in the viscoelastic mechanics. (e, f). In the β-MyHC, the ADP state is longer than that in the α-MyHC and the rigor state is more dramatically prolonged with decreasing MgATP compared to α-MyHC.