Grabarek Z, Drabikowski W, Leavis P C, Rosenfeld S S, Gergely J
J Biol Chem. 1981 Dec 25;256(24):13121-7.
Fragments of rabbit skeletal muscle Ca2+-binding subunit of troponin (TnC), obtained by cleavage with trypsin, thrombin, and CNBr, were tested for their ability to form binary and ternary complexes with ATPase inhibitory subunit (TnI) and tropomyosin-binding subunit (TnT) and their ability to replace TnC in reversing TnI inhibition of actomyosin ATPase activity. Three regions of TnC were found to be involved in interaction with TnI. Regions near Ca2+-binding sites II and III require Ca2+ for the interaction, while a third region near Ca2+-binding site IV binds TnI whether or not Ca2+ is present. The TnT binding site has been localized in the NH2-terminal half of TnC. Several of the TnC fragments form soluble ternary complexes with TnI and TnT. Fragments that contain amino acid residues 89-100 and at least one pair of Ca2+-binding sites are able to reverse the TnI inhibition of actomyosin ATPase activity, which exhibits the same [Ca2+]1/2 regardless of which of the Ca2+-binding sites are present in the fragment.
通过用胰蛋白酶、凝血酶和溴化氰切割获得的兔骨骼肌肌钙蛋白（TnC）的钙离子结合亚基片段，被测试了它们与ATP酶抑制亚基（TnI）和原肌球蛋白结合亚基（TnT）形成二元和三元复合物的能力，以及它们在逆转TnI对肌动球蛋白ATP酶活性的抑制作用中替代TnC的能力。发现TnC的三个区域参与与TnI的相互作用。钙离子结合位点II和III附近的区域在相互作用时需要钙离子，而钙离子结合位点IV附近的第三个区域无论是否存在钙离子都能结合TnI。TnT结合位点已定位在TnC的氨基末端一半区域。几个TnC片段与TnI和TnT形成可溶性三元复合物。包含氨基酸残基89 - 100和至少一对钙离子结合位点的片段能够逆转TnI对肌动球蛋白ATP酶活性的抑制作用，无论片段中存在哪个钙离子结合位点，其表现出相同的[Ca2+]1/2。
