Martin S R, Bayley P M
Biochem J. 1986 Sep 1;238(2):485-90. doi: 10.1042/bj2380485.
Near-u.v. and far-u.v. c.d. spectra of bovine testis calmodulin and its tryptic fragments (TR1C, N-terminal half, residues 1-77, and TR2C, C-terminal half, residues 78-148) were recorded in metal-ion-free buffer and in the presence of saturating concentrations of Ca2+ or Cd2+ under a range of different solvent conditions. The results show the following: if there is any interaction between the N-terminal and C-terminal halves of calmodulin, it has not apparent effect on the secondary or tertiary structure of either half; the conformational changes induced by Ca2+ or Cd2+ are substantially greater in TR2C than they are in TR1C; the presence of Ca2+ or Cd2+ confers considerable stability with respect to urea-induced denaturation, both for the whole molecule and for either of the tryptic fragments; a thermally induced transition occurs in whole calmodulin at temperatures substantially below the temperature of major thermal unfolding, both in the presence and in the absence of added metal ion; the effects of Cd2+ are identical with those of Ca2+ under all conditions studied.
在一系列不同的溶剂条件下，记录了牛睾丸钙调蛋白及其胰蛋白酶片段（TR1C，N端半段，第1至77位氨基酸残基；TR2C，C端半段，第78至148位氨基酸残基）在无金属离子缓冲液中以及在饱和浓度的Ca2+或Cd2+存在时的近紫外和远紫外圆二色光谱。结果表明：如果钙调蛋白的N端和C端半段之间存在任何相互作用，对任何一半的二级或三级结构都没有明显影响；Ca2+或Cd2+诱导的构象变化在TR2C中比在TR1C中要大得多；Ca2+或Cd2+的存在赋予整个分子以及任何一个胰蛋白酶片段对尿素诱导变性的相当大的稳定性；在添加金属离子和不添加金属离子的情况下，完整的钙调蛋白在远低于主要热解链温度的温度下都会发生热诱导转变；在所有研究条件下，Cd2+的作用与Ca2+相同。
