The reaction of thiol and disulphide groups with mercuric chloride and methylmercuric iodide. I. Simple thiols and soluble proteins

Abstract

The polarographic behaviour of MeHgCl, MeHgI, HgCl₂, neohydrin (3-chloromercuri-2-methoxypropylurea) and its iodo-derivative are described. Their chemical reactivity and -SH specificity have been investigated and MeHgI shown to have advantages as an -SH reagent on account of its high reactivity, stability, and " ideal " polarographic behaviour. The reaction of protein -SS- groups with Na₂SO₃ proceeds slowly to completion in the presence of HgCl₂ or MeHgI and it is shown that with bovine plasma albumin, ribonuclease, and insulin the polypeptide chains may be separated for preparative or structural studies under milder conditions than are customary. In the presence of urea at pH 9 the reaction is sufficiently rapid to form the basis of amperometric titration procedures for determining -SS- groups in eight intact proteins. The methods are especially valuable for proteins which have been previously converted to their -SR, -SO₃^-, or -SSO₃^-; derivatives since the destructive hydrolytic step may be avoided. The mechanism and stoichiometry of the reactions are discussed.