Thrombosthenin solubility

In 1959 Bettex-Galland and Liischer succeeded in extracting from human blood platelets such a (iontractile protein, which was subsecpiently named thrombosthenin. Its solubility properties, as well as its dependence for activity on the presence of ATP and metal ions, soon led to its classification as a member of the actomyosin group. Work on thrombosthenin has since continued, both with respect to its properties as a complex protein with enzymatic activity and to its biological significance. 

Thrombosthenin is extracted from a concentrated suspension of washed blood platelets obtained by any of the described methods of isolation (Maupin, 1954b). Bettex-Galland and Liischer (1961), starting with 50 liters of freshly (collected citrated human blood isolated by differential centrifugation in the (told, from the buffy layers, 20 to 30 ml of a highly concentrated suspension of washed platelets. Since the isolation of thrombosthenin is based on its solubility properties, special ce,re must be taken to eliminate the leucocytes their content of deoxyribonuclcoproteids... 

The presence of ATP leads to an increased solubility at lower ionic strength. Grette (1962) reports that solutions of porcine thrombosthenin tend toward precipitation at an ionic strength of only 0.08 g provided 5 X 10 M ATP is present. Perhaps it is not correct to speak of a solubilizing effect of ATP on thrombosthenin more likely this seemingly increased... 

Lowering the pH also leads to a decreased solubility of thrombosthenin. Grette (1962) obtained precipitation of porcine thrombosthenin at pH 6.5. The addition of small amounts of Mg++ ions seems to enhance the precipitating effect. Care must be taken, however, because even at pH 6 signs of progressive denaturation become discernible. It seems preferable for preparative purposes to work at a neutral pH. 

Based on such quantitative determinations of the viscosity changes induced by adding ATP to soluble thrombosthenin, the so-called ATP sensitivity of thrombosthenin has been calculated according to the method... 

The platelets contain a contractile protein (throm-bosthenin), which has solubility properties similar to those of the actomyosin group of proteins. The activity of the protein requires the presence of ATP and metallic ions. The protein has been isolated from human platelets, and like actinomycin, the contractile protein possesses ATPase activity. Electron microscopic examination of isolated thrombosthenin revealed a microfibric structure 80-100 A wide with a possible periodic structure [28]. In the presence of ATP, the contractile protein dissociates into an actinlike protein (thrombosthenin A) and a myosinlike (thrombosthenin M) moiety. ATPase activity is nonexistent in thrombosthenin A and weak in thrombosthenin M. When tested alone, neither thrombosthenin A or M is ATP sensitive, but the mixing of A and M thrombosthenin restores ATP sensitivity and ATPase activity. 

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