113 Cd NMR in the study of calcium binding proteins: Troponin C

摘要: Calcium is one of nature’s most versatile metal ions, for example some 70 calcium binding proteins have been described [ 11. However there exists a marked lack physical probes to study the properties Ca’+ in these molecules solution. Ca2’ diamag- netic and has no convenient optic spectroscopic properties. The magnetic isotope 43Ca(1 = S/2; natural abundance 0.145%) may principle be studied by NMR methods but direct observation 4sCa signals from probably ruled out large nuclear electric quadrupole moment 43Ca. Due very efficient relaxation signal expected broadened beyond detectability sites with less than cubic symmetry [2,3]. indirect method, i.e. small ions solu- tion that undergo reasonably fast chemical exchange macromolecular sites, proved informative such as Nat Cl- [4]. How- ever it not generally applicable Ca2* since if constant exceeds lo4 M-’ rate Ca” between protein solvent too slow at room temperature. ‘laCd recent years emerged useful tool zinc [S-9]. ‘13Cd spin I l/2 nucleus Cd’+ can often substitute Zn2+ enzymes least partial retention biological activity [lo]. ionic radius