Henzl M T, Birnbaum E R
Department of Chemistry, New Mexico State University, Las Cruces 88003.
J Biol Chem. 1988 Aug 5;263(22):10674-80.
The 7F0----5D0 transition of Eu3+ was used to probe the metal-binding domains of rat oncomodulin and rat parvalbumin. Two distinct differences between the two proteins were observed. The first relates to the pH-dependent behavior of their 7F0----5D0 spectra, a phenomenon noted previously for other paravalbumins. In the case of rat parvalbumin, the spectral features associated with both metal-binding sites titrate concomitantly (pK alpha = 8.2); however, in the case of oncomodulin, the two sites titrate sequentially (pK alpha = 6.3 for the CD site; pK alpha = 8.3 for EF site). The proteins also contrast with regard to their discrimination for Eu3+ over Ca2+. The CD and EF sites in rat parvalbumin both display a large preference for Eu3+: (KCa/KEu)CD = 143 +/- 11 and (KCa/KEu)EF = 191 +/- 30. However, in the case of oncomodulin, although the EF site of oncomodulin greatly prefers the trivalent lanthanide ion (KCa/KEu = 300 +/- 80), the CD site exhibits a relatively minor preference (KCa/KEu = 11 +/- 1).
利用铕离子（Eu3+）的7F0----5D0跃迁来探测大鼠癌调蛋白和大鼠小清蛋白的金属结合结构域。观察到这两种蛋白质之间存在两个明显差异。第一个差异与它们7F0----5D0光谱的pH依赖性行为有关，这一现象先前在其他小清蛋白中也有发现。对于大鼠小清蛋白，与两个金属结合位点相关的光谱特征同时滴定（pKα = 8.2）；然而，对于癌调蛋白，两个位点依次滴定（CD位点的pKα = 6.3；EF位点的pKα = 8.3）。这两种蛋白质在对Eu3+和Ca2+的区分上也存在差异。大鼠小清蛋白的CD和EF位点都对Eu3+有很大偏好：（KCa/KEu）CD = 143 ± 11，（KCa/KEu）EF = 191 ± 30。然而，对于癌调蛋白，虽然癌调蛋白的EF位点非常偏好三价镧系离子（KCa/KEu =
