Troponin from smooth adductor muscle of Ezo-giant scallop

Troponin which can confer Ca2+-sensitivity upon rabbit actomyosin Mg-ATPase activity has been prepared from the smooth adductor muscle of Ezo-giant scallop (Patinopecten yessoensis). The troponin comprises 40-, 20-, and 19-kDa components. In order to characterize the components, they were separated from each other by CM-Toyopearl column chromatography in the presence of 6 M urea. Consequently, the 20-kDa component was identified as troponin C, based on the Ca2+-binding ability. The amount of Ca2+ bound to the troponin C was estimated to be 0.75 mol/mol at 10(-4) M Ca2+ by the equilibrium dialysis method. The 19-kDa component was identified as troponin I on the basis of not only its inhibitory effect on rabbit actomyosin Mg-ATPase activity along with the smooth adductor tropomyosin, but also the releasing effect of the smooth adductor troponin C on the inhibition. On the other hand, the 40-kDa component was regarded as troponin T on the basis that it bound to F-actin-tropomyosin filament and was indispensable for conferring Ca2+-sensitivity upon rabbit actomyosin Mg-ATPase activity, along with troponin C and troponin I. The above assignments were confirmed by both amino acid analysis and immunoblotting using rabbit antisera raised against counterparts of scallop striated muscle troponin.