Simultaneous Reduction and Mercuration of Disulfide Bond aA-A11 of Insulin by Monovalent Mercury

Insulin reacts with monovalent mercury ions in 0.5 m aqueous acetic acid. Two atoms of mercury are incorporated per protein molecule; only one atom is, however, retained upon gel filtration of the product. It was shown that the mercurous ions selectively reduce and mercurate the disulfide bridge A6-A11 of the protein, forming an S-Hg-S bond. The insulin-mercury complex which is designated [insulin·Hg] is monomeric, behaves on electrophoresis like the native protein, exhibits full combining power with anti-insulin, and exhibits a circular dichroism (CD) spectrum in the region of peptide absorption which is very similar to that of native insulin. The conformation of the insulin-mercury complex is thus similar to that of the native protein. The possible application of the above reaction for the preparation of heavy atom derivatives of proteins for X-ray studies is discussed.