Molecular friction in an actomyosin molecular machine.

In muscle contraction, it has been widely recognized that a binding state exists between myosin and actin in the presence of Mg-ATP. To estimate the magnitude of binding strength, I introduce a concept of frictional phenomena which occurs between two sliding bodies in contact each other. In such cases, the sliding speed can be formulated as a function of the actin-myosin bond strength. In order to validate this, the present theory is applied for the two movement assay systems with no external load; one movement assay of Phalloidin Rhodamine bound F-actin on a myosin coated hydrophobic cover glass and another assay of myosin coated beads along actin cables of Nitella. If a coefficient of 0.005 is applied to the kinetic friction, 1pN for the sliding force per cross-bridge and 10 microns sec-1 for the sliding speed, it is found that the bond strength between actin and one myosin head is about 200 pN in the contracting state.