The stiffness of the crossbridge is a function of the intrinsic protein osmotic pressure generated by the crossbridge itself

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Abstract
A model is presented that makes it possible to determine the stiffness of the crossbridge from protein osmotic stress experiments. The model was elaborated while studying the osmotic properties of F‐actin and of myosin subfragment‐1 F‐actin. These studies showed that the elastic modulus by bending of the monomer is directly related to the intrinsic protein osmotic pressure of the system. At a protein osmotic pressure of 1.8 × 105dynes/cm2, the physiological protein osmotic pressure of frog skeletal muscle, it was found that the elastic moduli by bending of the monomer in F‐actin and in the myosin subfragment‐1 decorated F‐actin are 6.5 × 107 and 3.3 × 108 dynes/cm2, respectively. The value of the elastic modulus by bending of the monomer in the myosin subfragment‐1 decorated F‐actin compares favorably with the values of the elastic modulus by stretching determined in skeletal muscle fibres.