Electrosynthetic modification of proteins: Electrooxidations at methionine and tryptophan in hen egg-white lysozyme

Electrosynthesis provides a novel methodology to produce specific and selective chemical reaction in proteins. Thus electrooxidation of hen egg-white lysozyme (HEWL) at + 1.2 V (vs sce) at a carbon anode in mildly acid buffer produces selective oxidation at methionine-105; while by increase in anodic potential, or by addition of acetonitrile co-solvent, subsequent oxidation at methionine-12 is observed. Further increase of potential in otherwise similar conditions additionally produces a novel cleavage between tryptophan-62 and tryptophan-63, the latter remaining intact and becoming the new N-terminus of the fragment. No reaction occurs at other tryptophan residues in HEWL, and histone H4, which contains no tryptophan residues, does not cleave in these conditions. The previously reported selective nitration at tyrosine residues by use of copper electrodes in alkaline medium is not observed in the acid electrolysis system and shows the fine control over protein modification available by manipulation of electrosynthetic parameters. The methodology offers wide implications. (C) Elsevier Science Ltd.