Interaction of enkephalin derivatives with reactive oxygen species

The oxidation of opioid peptides by tyrosinase in the presence of an excess of a thiol gives rise to cysteinyldopa derivatives. The major products ari sing from the reaction between Leu-enkephalin and cysteine are represented by 5-S-cysteinyldopaenkephalin (5-CDenk) and 2-S-cysteinyldopaenkephalin (2 -CDenk). The interaction of 5-CDenk and 2-CDenk with reactive oxygen specie s (ROS) has been studied. These compounds are able to scavenge superoxide a nion, hydroxyl and peroxyl radicals as well as to reduce the lipid peroxida tion rate induced by ABAP. The scavenging activities in all instances are d ose-dependent. In some cases CDenks are more active than compounds recogniz ed as strong radical scavengers, such as Trolox and mannitol. As a result o f the action of the Fenton system, the CDenks (as well as the Enks) are oxi dized into pigmented derivatives. The possible implications of the interact ion of CDenks and Enks with ROS on melanization process in Parkinson's dise ase are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.