Thrombosthenin, the Contractile Protein from Blood Platelets and Its Relation to other Contractile Proteins

Publisher Summary This chapter deals primarily with the contractile protein from human blood platelets, which is named “thrombosthenin,” in view of its origin and function. It also reviews blood platelets in general and their role in hemostatis. The role of thrombosthenin for platelet function is addressed and its properties are compared with those of other contractile proteins. This chapter illustrates that these proteins are soluble only at an elevated ionic strength, they show ATP sensitivity as well as the phenomenon of superprecipitation and they are all active as ATPases. The enzymatic activities of the contractile proteins from striated muscle, from smooth muscle, and from tumor cells or blood platelets differ markedly from each other. Furthermore, it is of particular interest to note that the relaxing factor obtained from striated muscle does not affect contractile models of smooth muscle and most likely is also ineffective against tumor-cell models. Subsequently, it has generally been assumed that the energy required for muscular contraction has been derived directly from the ATP split in the course of the reaction. The availability of thrombosthenin with its much lower ATPase activity might be an interesting material for a comparative investigation of this basically important mechanism. Thus, thrombosthenin may prove not only interesting with respect to the functions of the blood platelets but also with respect to the general importance of the elucidation of many remaining problems in the field of the contractile proteins.