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Nuclear Magnetic Resonance Studies of the Complex Formation of Mercuric Chloride with L-Cysteine and with Glutathione

The binding of mercuric chloride, HgCl2, with an amino acid, L-cysteine, and with a tripeptide, glutathione, as a model for sulfhydryl proteins, has been investigated by proton and carbon-13 magnetic resonance spectroscopy. Binding to the active coordination sites was monitored, while observing the chemical shifts of protons and carbon nuclei of the ligand in various conditions of the molar ratio (HgCl2/ligand). The results indicate that mercuric chloride binds exclusively to the sulfhydryl group both in L-cysteine and glutathione. A weak secondary binding may also take place with the carboxylic acid group to some extent in the former and with the cysteinyl carbonyl group in the latter, respectively, up to equimolar point. It is also concluded that the stability of the binding of mercuric chloride depends on the pD of the solution. The results are discussed in terms of possible complex structure.