Interactions and Transport of Charged Species in Bulk and at Interfaces
An Ionic-Chemical-Mechanical Model for the Actin-Myosin ATPase Cycle in Muscle ContractionGerald S. Manning
The dynamic process underlying muscle contraction is the parallel sliding of thin actin filaments along an immobile thick myosin fiber powered by myosin protrusions acting as motorized cross bridges. The energy for functioning of the nanomotor comes from the hydrolysis of bound ATP. The unit step of translational movement is based on a mechano-chemical cycle involving ATP binding to myosin, hydrolysis of the bound ATP, conformational changes in the myosin head, and release of hydrolysis products. Current knowledge indicates that electrostatic interactions among the multitude of ionized amino acid residues of both actin and myosin are involved in the progress of the cycle. The actin filament is an anionic (net negatively charged) polyelectrolyte surrounded by a sheath of condensed counterions. We employ well-documented aspects of polyelectrolyte theory to suggest how actin-myosin electrostatic interactions might be of significance in the modulation of forces during the cycle. We provide quantitative force estimates that are in the pN range known to operate in the cycle.