[Dependence of the rate of myofibril contraction on MgATP concentration. A theoretical examination].

We propose simple model for the mechano-biochemical cycle of the myosin cross-bridges, taking into account the contribution of "slow binding" bridges in the negative strength. Mathematical analysis of this model allows us to obtain an analytical expression for the dependence of the contraction velocity on the MgATP concentration. Parameters of this equation are rate constants of dissociation of "slow binding" bridges from thin filament, liberation of inorganic phosphate and binding of MgATP. The model leads to the bell-shaped dependence of myofibrillar contraction velocity on the substrate concentration similar to the experimental one. The values of above mentioned constants for the isolated myofibrils are estimated to be close to values obtained in unstructured contractile models.