Thrombosthenin superprecipitation

This phenomenon, termed superprecipitation by Szent-Gyorgyi (1951), is typical for the contractile proteins of the actomyosin group. It becomes even more spectacular if concentrated solutions of thrombosthenin are spun out to small fibers and allowed to shrink (Bettex-Galland and Luscher, 1961). Precipitates obtained from dilute solutions are not stable enough to show macroscopically visible contraction. In this case a fine granular... 

The speed of the contraction of a superprecipitate is greatly dependent upon temperature. For thrombosthenin at room temperature (about 20°C) 15 to 20 min are required for complete contraction. At 37°C this process requires only 1 to 2 min. At 0°C superprecipitation does not take place. Accurate and comparable measurements of the contraction rates... 

Tephorine and Diparcol, both synthetic antihistamines known to inhibit clot retraction (Bounameaux, 1957 Hugues, 1959), only partially inhibit ATPase activity and superprecipitation of thrombosthenin. Finally, monoiodoacetate, a powerful inhibitor of clot retraction, inhibits neither phenomenon. 

The findings reported above may be summarized as follows Inhibitors of the ATPase activity of thrombosthenin always are inhibitors of superprecipitation, whereas they do not necessarily affect manifestations of the contractile activity of the whole platelet, such as clot retraction, to the same extent. 

At low ionic strengths, ATP causes the superprecipitation of thrombosthenin. Applied at higher ionic strength, i.e., under conditions where the protein is in solution, it exerts an entirely different effect—it causes the dissociation of the thrombosthenin complex into its two components. This dissociation is connected with a considerable decrease in viscosity that is easily determined quantitatively. 

Recently, Grette (1963) has reported the extraction from pig platelets of a material with properties comparable to the relaxing factor from muscle (Marsh, 1951). Solutions of this factor will inhibit superprecipitation as well as ATPase activity of thrombosthenin of porcine origin. Calcium ions, on the other hand, were found to inhibit this relaxing effect. 

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