title: Ultracentrifugation study on interactions among calmodulin, cardiac troponin and tropomyosin-actin complex.
abstract: In an effort to clarify the regulation of contractions in cardiac muscle, we performed ultracentrifugation studies on the interactions between cardiac troponin and tropomyosin-actin complex in the presence of Ca2+ or Sr2+. When troponin C and troponin I were centrifuged with tropomyosin-actin complex, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Troponin C was observed to bind very weakly to troponin T-tropomyosin-actin complex in either the presence of absence of bivalent-cation. When troponin C was replaced by calmodulin, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Calmodulin bound to the troponin I-troponin T-tropomyosin-actin complex only in the presence of bivalent-cation. These results suggest that the inhibitory action of troponin I is neutralized by troponin C or calmodulin upon binding of bivalent-cation while troponin I binds to tropomyosin-actin complex in cardiac muscle. Therefore cardiac muscle seems to differ from skeletal muscle in regard to regulation of its contraction.
authors.affiliation: Health Services Center, Kyushu Institute of Design, Fukuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
authors.forename: K
authors.initials: K
authors.lastname: Nunoi
authors.forename: M
authors.initials: M
authors.lastname: Fujishima
mesh_terms: D000199:Actins / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D002147:Calmodulin / Q000032:analysis / Q000378:metabolism*; D006321:Heart / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000032:analysis / Q000378:metabolism; D013552:Swine; D014335:Tropomyosin / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D014336:Troponin / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D014461:Ultracentrifugation
chemical_list: D000199:Actins; D002147:Calmodulin; D014335:Tropomyosin; D014336:Troponin