Identification of Myosin A, Actin and Native Tropomyosin Constituting of Arterial Contractile Protein (Myosin B) and Their Characteristics

抄録

In order to clarify the characteristic features of arterial contractile protein, natural actomyosin (myosin B), myosin A, actin and native tropomyosin were extracted from bovine carotid arteries and their characteristic features were compared with those from bovine cardiac muscle and from rabbit's skeletal muscle. In this study, the following points were clarified: l) Arterial contractile protein mainly consisted of myosin A, actin and native tropomyosin, regulatory protein respondent to Ca²⁺ just as having been observed in those from striated muscle. 2) Arterial myosin A, actin and native tropomyosin possessed the similar features characteristic of myosin A, act-in and native tropomyosin from striated muscle, respectively, as shown with following items; effect of divalent cations on ATP-ase activity of myosin A, G&nrarr;F transformation in actin the formation of "arrow-head structure" m F-actin by reaction with arterial and skeletal H-meromyosins and the demonstration of the intraction of myosin A and F-actin with regardless of their origins. 3) The optimal concentration of Mg²⁺ necessary for the interaction of myosin A and F-actin was much high (10-20 mM) in myosin A from arterial wall and very low (< 0.5 mM) in myosin A from striated muscle regardless of origin of the F-actin. 4) In electronmicrographic structures, arterial myosin aggregates were shorter in the length compared with that of striated muscle, having rod shape without tapering and possessed the fine projections only at the both ends. However, any difference has not been observed between arterial F-actin and F-actin from striated muscle which held helical structure with the pitch of about 350 A and the width of about 80 A. 5) The thin filaments containing actin were located not only at muscular layer of arterial wall but also at endothelium of renal capillary. Through the above findings, it was understood that the contraction - relaxation of arterial wall, even in capillary, contributory to the performance of blood circulation was based on the association - dissociation of myosin aggregate and F-actin together with native tropomyosin respondent to Ca²⁺ through increase - decrease of Ca²⁺, which is associated with hydrolysis of ATP in the presence of Mg²⁺.