Dj. Walton et al., ELECTROSYNTHETIC MODIFICATION OF PROTEINS - ELECTROOXIDATIONS AT METHIONINE AND TRYPTOPHAN IN HEN EGG-WHITE LYSOZYME, Electrochimica acta, 42(15), 1997, pp. 2285-2294
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 mil
dly acid buffer produces selective oxidation at methionine-105; while
by increase in anodic potential, or by addition of acetonitrile co-sol
vent, subsequent oxidation at methionine-12 is observed. Further incre
ase 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 r
eaction occurs at other tryptophan residues in HEWL, and histone H4, w
hich contains no tryptophan residues, does not cleave in these conditi
ons. 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 modif
ication available by manipulation of electrosynthetic parameters. The
methodology offers wide implications. (C) Elsevier Science Ltd.