[Structural-functional alterations in contractile proteins in athyreotic dystrophy of the myocardium].

In athyreotic dystrophy of the heart muscle properties both actin- and myosin-containing fibers protein components are shown to change. Changes in actin-containing filaments become apparent in a decrease in superprecipitation value of hybrid actomyosin consisting of athyreotic actin and myosin from normal myocardium. Disturbances in myosin structure result in a decrease of both, the value and rate of hybrid actomyosin superprecipitation consisting of athyreotic myosin and normal actin. The value of Mg2+-ATPase activity of hybrid actomyosins does not practically differ from that of normal actomyosin. Native athyreotic tropomyosin loses its ability to activate Mg2+-ATPase of purified actomyosin but its Ca2+ sensitivity, as well as its ability to increase the superprecipitation rate of normal actomyosin do not change. The obtained data suggest that a decrease in a tension value developed by bundles of glycerinated muscle fibers of athyreotic myocardium results from changes in the properties of both actin and myosin, while a reduction in the rate of fiber contraction is caused by disturbances of myosin properties and may be of native tropomyosin as well.