Dynamic viscoelastic study of acto-heavy meromyosin in solution

Abstract

The dynamic rigidity modulus ( G′) and loss modulus ( G″) of acto-heavy meromyosin solutions were measured under various conditions. When the protein concentrations were 3 mg/ml for F-actin and 8.1 mg/ml for heavy meromyosin, the value of G′ was more than 1500 dynes/cm 2 in the presence of 0.1 M KCl, whereas that of G″ was less than 500 dynes/cm 2. The value of G′ dropped to a low value of 50 dynes/cm 2 on addition of ATP, and then it gradually increased reaching a value three times as large as the initial one after the hydrolysis of ATP. Comparing the G′ value of acto-heavy meromyosin solution with those of acto-subfragment I and acto-3-S myosin, we concluded that F-actin filaments were cross-linked by the two heads of each heavy meromyosin molecule and thus a continuous network was formed in solution, which resulted in the increase in the value of G′. The network of acto-heavy meromyosin was shown to be easily broken by a weak external force. From the temperature dependence of G′ of the acto-heavy meromyosin solution, it was suggested that the network formed by acto-heavy meromyosin particles in solution was rubber-like. The increase in solution viscosity due to actomyosin formation was explained by the same reasoning as in the increase in dynamic rigidity modulus.