A Binary Complex of Troponin-I and Troponin-T from Akazara Scallop Striated Adductor Muscle

Abstract

A binary complex consisting of M_r 19, 000 and M_r 40, 000 components was co-purified with troponin from a crude troponin fraction of Akazara scallop (Chlamys nipponensis akazara) striated adductor muscle. This complex is incapable of conferring Ca²⁺-sensitivity to rabbit reconstituted actomyosin Mg-ATPase activity, rather strongly inhibiting it, but became capable on further complexing with Akazara scallop troponin-C. To examine the effects of the M_r 19, 000 and M_r 40, 000 components on the ATPase activity, they were separated from each other by CM-Toyopearl column chromatography. The M_r 19, 000 component strongly inhibited the Mg-ATPase activity of actomyosin-tropomyosin and the inhibition was reversed by further addition of the Akazara scallop troponin-C. On the other hand, the M_r 40, 000 component slightly increased it. On hybridization with the Akazara scallop troponin subunits, the M_r 19, 000 and M_r 40, 000 components were shown to be able to substitute for troponin-I and troponin-T, respectively. The amino acid compositions of the M_r 40, 000 component and troponin-T were almost identical, and those of the M_r 19, 000 component and M_r 17, 000 C-terminal fragment of the troponin-I resembled each other fairly well. From these results, it may be concluded that the M_r 19, 000-40, 000 binary complex is the troponin-I-troponin-T complex.