[Hyperthyreosis Inhibits the Ability of Actin to Form Strong-Binding with Myosin].

The effect of hyperthyreosis development induced by the increase in thyroid hormones in rats (during 2-4 weeks) on the orientation and mobility of fluorescent probe N-(iodoacetyl)-(1-naphtyl-5-sulpho-ethylenediamine) specifically bound to Cys 374 of actin in ghost muscle fibers isolated from fast (EDL) and slow (SOL) rat muscles was studied. It was found that the binding of myosin subfragment-1 (S1) to F-actin induced the typical for the formation of strong binding actomyosin decrease in mobility of actin subdomain 1 and its rotation towards thin filament periphery. Development of hyperthyreosis markedly inhibited these phenomena. The maximal effect was observed after 21 days of disease development. It is suggested that one of the reasons of the contractile deficit of muscle in hyperthyreosis is inhibition of the strong binding between actin and myosin during ATPase cycle.