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Author Ellis, P. D. ♦ Strang, P. ♦ Potter, J. D.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword RADIOLOGY AND NUCLEAR MEDICINE ♦ BASIC BIOLOGICAL SCIENCES ♦ CADMIUM 113 ♦ NMR SPECTRA ♦ CADMIUM COMPOUNDS ♦ CONFIGURATION INTERACTION ♦ PROTEINS ♦ BIOCHEMISTRY ♦ CATIONS ♦ NUCLEAR MAGNETIC RESONANCE ♦ SKELETON ♦ TROPOMYOSIN ♦ BETA DECAY RADIOISOTOPES ♦ BETA-MINUS DECAY RADIOISOTOPES ♦ BODY ♦ CADMIUM ISOTOPES ♦ CHARGED PARTICLES ♦ CHEMISTRY ♦ EVEN-ODD NUCLEI ♦ INTERMEDIATE MASS NUCLEI ♦ IONS ♦ ISOMERIC TRANSITION ISOTOPES ♦ ISOTOPES ♦ MAGNETIC RESONANCE ♦ NUCLEI ♦ ORGANIC COMPOUNDS ♦ ORGANS ♦ RADIOISOTOPES ♦ RESONANCE ♦ SPECTRA ♦ STABLE ISOTOPES ♦ YEARS LIVING RADIOISOTOPES ♦ Medicine- Unsealed Radionuclides in Diagnostics ♦ Biochemistry- Tracer Techniques
Abstract The binding of cadmium to skeletal troponin C (STnC) has been measured in two ways. Equilibrium binding experiments have shown two cadmium binding sites on STnC with a high affinity for Cd/sup 2 +/ and two with a lower affinity for Cd/sup 2 +/. The former binding constant is comparable to Ca/sup 2 +/ binding to the Ca/sup 2 +/-Mg/sup 2 +/ (structural) sites of STnC; the latter is about a factor of one hundred less than Ca/sup 2 +/ binding to the Ca/sup 2 +/-specific (regulatory) sites of STnC. In the presence of Mg/sup 2 +/ the affinity of Cd/sup 2 +/ for the higher affinity sites was lowered. These data clearly suggest that the sites with high affinity for Cd/sup 2 +/ are the same as the Ca/sup 2 +/-Mg/sup 2 +/ sites. The /sup 113/Cd NMR is temperature-dependent. At room temperature two resonances at -107.8 and -112.7 ppm are seen. Lowering the temperature to 4/sup 0/C alters the cadmium exchange dynamics, and results in a four line /sup 113/Cd spectrum. The two new resonances probably arise from cadmium binding to the Ca/sup 2 +/-specific sites on STnC; whereas, the resonances at -107.8 and -112.7 ppm correspond to cadmium binding at the Ca/sup 2 +/-Mg/sup 2 +/-sites, respectively. When the /sup 113/Cd/sup 2 +/-substituted protein was titrated with Ca/sup 2 +/, the two resonances of the high affinity sites were reduced, followed by a reduction of the lower affinity Cd/sup 2 +/ sites. Since the direct binding experiments demonstrate that the high affinity Cd/sup 2 +/ sites are the Ca/sup 2 +/-Mg/sup 2 +/ sites, it is concerned that Cd/sup 2 +/ binding to the protein dramatically alters the affinity of the Ca/sup 2 +/-Mg/sup 2 +/ sites for Ca/sup 2 +/ possibly with allosteric coupling network between binding sites.
Educational Use Research
Learning Resource Type Article
Publisher Date 1984-08-25
Publisher Place United States
Journal J. Biol. Chem.
Volume Number 259
Issue Number 16
Organization Univ. of South Carolina, Columbia


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