Interactions of Muscle β-Connectin with Myosin, Actin, and Actomyosin at Low Ionic Strengths1

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Abstract
The interaction of the muscle elastic protein connectin with myosin and actin filaments was investigated by turbidimetry, viscosity, flow birefringence measurements, and electron microscopic observations. In KCl concentrations lower than 0.15 M at pH 7.0 at 25°C, both myosin and actin filaments were aggregated by connectin. Myosin filaments were entangled with each other in the presence of connectin. Actin filaments were assembled into bundles under the influence of connectin just as under that of α-actinin. The physiological significance of the interactions of connectin with myosin and actin filaments is discussed in relation to the localization of connectin in myofibrils. The Mg 2+ -activated ATPase activity of actomyosin was appreciably enhanced by connectin in the presence of KCl concentrations lower than 0.1 M. The extent of activation by connectin was smaller than by α-actinin. The enhancement of the ATPase activity may be due to acceleration of the onset of superprecipitation of actomyosin.