Burtnick L D, McCubbin W D, Kay C M
Can J Biochem. 1975 Jan;53(1):15-20. doi: 10.1139/o75-003.
TN-C was purified from bovine cardiac muscle. In the absence of Ca-2+, cardiac TN-C has an intrinsic sedimentation coefficient of 1.93 S and a molecular weight of 18 000 daltons. Cardiac TN-C reverses the inhibitory effect of skeletal TN-I on the Mg-2+-activated ATPase of a skeletal synthetic actomyosin preparation in the presence of skeletal tropomyoson. Circular dichroism (CD) studies indicate that cardiac TN-C undergoes a major conformational change upon binding Ca-2+. A similar response is elicited by Sr-2+, whereas Mg-2+ has a much less pronounced effect. The presence of Mg-2+ does not alter the net effects of either Ca-2+ or Sr-2+. Cardiac TN-C is rich in acidic amino acid residues. UV absorption, near UV CD, and fluorimetric studies show that the protein lacks tryptophan and has a relatively high phenylalanine to tyrosine ratio. The results of this study invite direct comparisons with results reported for the skeletal muscle analogue of cardiac TN-C.
TN-C是从牛心肌中纯化得到的。在没有Ca2+的情况下，心脏TN-C的固有沉降系数为1.93 S，分子量为18000道尔顿。在存在骨骼肌原肌球蛋白的情况下，心脏TN-C可逆转骨骼肌TN-I对骨骼肌合成肌动球蛋白制剂的Mg2+激活的ATP酶的抑制作用。圆二色性（CD）研究表明，心脏TN-C在结合Ca2+时会发生主要的构象变化。Sr2+也会引发类似的反应，而Mg2+的作用则不那么明显。Mg2+的存在不会改变Ca2+或Sr2+的净效应。心脏TN-C富含酸性氨基酸残基。紫外吸收、近紫外CD和荧光研究表明，该蛋白质不含色氨酸，苯丙氨酸与酪氨酸的比例相对较高。本研究结果促使人们将其与心脏TN-C的骨骼肌类似物的报道结果进行直接比较。
