Akazara scallop troponin C: Ca(2+)-induced conformational change and interaction with rabbit troponin subunits.
The number of specific Ca2+ bound to Akazara scallop troponin C was estimated to be 0.7 with an apparent binding constant of 5 x 10(5) M-1 (T. Ojima and K. Nishita, 1986, J. Biol. Chem. 261, 16749-16754). In the present paper, we report on the Ca(2+)-induced conformational changes in the troponin C and the interaction of the troponin C with rabbit troponin subunits. The Ca2+ binding to the troponin C caused a marked change in difference uv absorption spectra and a retardation of elution on Sephacryl S-200 gel filtration. However, its circular dichroism spectrum was hardly changed by the Ca2+ binding. These results suggest that the Ca2+ binding to the troponin C induced changes predominantly in tertiary structure rather than in secondary structure. Akazara scallop troponin C was shown to be able to bind to rabbit troponin I-Cellulofine affinity column, but the affinity was not greatly increased by Ca2+ unlike the case of rabbit troponin C. On hybridizing with rabbit troponin T and I, Akazara scallop troponin C was shown to be incapable of substituting rabbit troponin C; i.e., the hybrid troponin strongly inhibited the Mg-ATPase activity of rabbit actomyosin-tropomyosin irrespective of the presence or absence of Ca2+, thus recovering no Ca2+ sensitivity.
Ojima
T
T
Department of Chemistry, Faculty of Fisheries, Hokkaido University, Japan.
Nishita
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry; D002850:Chromatography, Gel; D002942:Circular Dichroism; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008974:Mollusca / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D013045:Species Specificity; D013056:Spectrophotometry, Ultraviolet; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T
D002135:Calcium-Binding Proteins; D046911:Macromolecular Substances; D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T; D002118:Calcium