Flexibility of myosin rod determined from dilute solution viscoelastic measurements

• Published in: Biochemistry (Easton) 1982-08, Vol.21 (17), p.4064-4073
• Main Authors: Hvidt, Soeren, Nestler, F. Henry M, Greaser, Marion L, Ferry, John D
• Format: Article
• Language: English
• Subjects: Animals; Circular Dichroism; Elasticity; Glycerol; Myosins - isolation & purification; Rabbits; Solutions; Spectrophotometry, Ultraviolet; Viscosity
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00260a024

The frequency dependencies of the storage and loss shear moduli, G' and G", of myosin rod solutions at 1.0 and 7.0 degrees C were measured by use of the Birnboim-Schrag multiple lumped resonator apparatus in solvents with and without glycerol. The infinite dilution moduli were determined and compared with theoretical models for a rigid rod and a freely jointed trinodular rod and with an empirical model for a semiflexible rod. Only the latter could fit the data. A rotational relaxation time of 25 mus and a slowest bending time of 3.1 mus, both reduced to water at 20 degrees C, were determined from the fit. A persistence length of about 130 nm was obtained from either the bending time, the rotational relaxation time, or the intrinsic viscosity. The average thermal excursion of the end of subfragment 2 was estimated to be 26 nm, more than sufficient to span the gap between the thick and thin filaments in muscles at all sarcomere lengths. Thus, a hinge between heavy meromyosin and light meromyosin does not appear necessary for myosin-actin contact. Young's modulus of about 1 x 10(9) N/m2 also makes it unlikely that subfragment 2 can be the elastic element in the Huxley-Simmons model of muscle contraction.