Thrombosthenin isolation

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... 

Thrombosthenin M was isolated from thrombosthenin by the use of polyethenesulfonate. This compound belonging to the group of interaction inhibitors (Bdrdny and Jaisle, 1960) potentiates the dissociation at such a low ionic strength that thrombosthenin M precipitates, whereas... 

An alternative way of preparing thrombosthenin A uses the supernatant from the isolation of thrombosthenin M as a starting material. This solution is first concentrated and low molecular components are removed by gel filtration. This method has not yet been used to any great extent for preparative purposes (Bettex-Galland et al., 1963a). 

The discussion of the similarities and dissimilarities of thrombosthenin and other contractile proteins will be restricted to the group of actomyosin-like proteins. As already mentioned, contractile substances of other types have not yet been isolated in a purified form and most of our knowledge about them comes from studies of glycerol-extracted cell models, which have not yet been prepared from blood platelets. Lastly, there can be little doubt that the mode of action of these other systems must be quite different from thrombosthenin. 

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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