title: Regulatory mechanism in arterial smooth muscle contraction.
abstract: The regulatory mechanism in the aortic actomyosin system was studied. Superprecipitation of desensitized aortic myosin B was not exhibited even in the presence of Ca2+, but was observable only in the presence of native tropomyosin and Ca2+. Reconstituted actomyosin composed of pure aortic myosin and pure skeletal actin did not show superprecipitation. Addition of aortic native tropomyosin and Ca2+ caused a marked superprecipitation. The ATPase of reconstituted actomyosin was enhanced three- or fourfold by aortic native tropomyosin and Ca2+. The extent of superprecipitation of aortic myosin B did not show a biphasic type of response to Mg-ATP concentration. Thus, aortic native tropomyosin induces a real activation of the myosin, actin, and ATP system in the presence of Ca2+, in contrast with the case of skeletal native tropomyosin, which induces the depression of skeletal myosin-actin-ATP interaction in the absence of Ca2+.
mesh_terms: D000205:Actomyosin / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009119:Muscle Contraction; D009218:Myosins / Q000378:metabolism; D014335:Tropomyosin / Q000378:metabolism
chemical_list: D014335:Tropomyosin; D004533:Egtazic Acid; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium; D002118:Calcium