Studies on the superprecipitation of actomyosin in isoproterenol-induced cardiac hypertrophy.

Superprecipitation of normal and hypertrophic cardiac actomyosin--made from individually purified cardiac myosin and skeletal F-actin-, compared with that of synthetic skeletal actomyosin was investigated. A proportional relationship was found between the extent maximum of superprecipitation (Emax) and the concentration of actomyosin complex in the range of 0.1-0.5 mg protein/ml. At 3 X 10(-5) M ATP the Emax was higher in the case of skeletal actomyosin than ardiac actomyosin. At 1.5 X 10(-4) M ATP the superprecipitation was preceded by clearing phase and the time required for the half-maximal increase of turbidity (t//2) was longer for cardiac actomyosin than skeletal actomyosin. The superprecipitation was promoted by decreasing Mg2+ concentration, while the increase in Mg2+ concentration inhibited the superprecipitation and caused the prolongation of clearing phase. The decreased superprecipitation of the actomyosin from hypertrophied hearts and the narrower potassium chloride concentration range, in which the superprecipitation took place, may be the consequence of the significantly lower ATPase activity.