NMR Studies of Crab and Plaice Metallothioneins

• Published in: Environmental health perspectives Vol. 65; pp. 157 - 165
• Main Authors: Higham, Denise P., Nicholson, Jeremy K., Overnell, Julian, Sadler, Peter J.
• Format: Journal Article
• Language: English
• Published: United States National Institute of Environmental Health Sciences. National Institutes of Health. Department of Health, Education and Welfare 01-03-1986
• Subjects: Amino acids; Animals; Binding sites; biochemical composition; Brachyura - physiology; Cadmium; Calcium; Cancer pagurus; Conference on High Affinity Metal-Binding Proteins in Non-Mammalian Species, September 19-21, 1984, Research Triangle Park, North Carolina; Edetic Acid; Fishes - physiology; hepatopancreas; Kinetics; Liver; Magnetic Resonance Spectroscopy; Marine; marine crustaceans; marine fish; Metal ions; Metallothionein; N.M.R; Pleuronectes platessa; Proteins; Protons; Spectroscopy; Zinc
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.8665157

Metallothioneins isolated from the hepatopancreas of the edible crab (Cancer paqurus) and the plaice (Pleuronectes platessa) after cadmium injection are predominantly cadmium proteins containing only small amounts of zinc and traces of copper. The removal of metal ions from the two metallothioneins by EDTA was studied using proton NMR spectroscopy. The rates of removal of cadmium and zinc were monitored directly from the intensity of the resonances due to the cadmium and zinc-EDTA complexes. Nearly all the zinc present in the protein was extracted by EDTA relatively rapidly, whereas only 10 to 20% of the total cadmium was removed in at least three steps. The total (Cd + Zn) metal removed at equilibrium was 1.2 to 1.8 g-ions/mole protein. Information on conformational changes in the protein were also obtained from studying alterations in the proton resonances of the protein. This was directly correlated with removal of metal from the protein. The coordination environments of the cadmium ions in crab metallothionein were investigated by using113Cd- NMR, and compared with113Cd- NMR spectra of rabbit liver MT-II and Scylla serrata MT-I.