GENERATION OF SUPEROXIDE AND TYROSINE PEROXIDE AS A RESULT OF TYROSYLRADICAL SCAVENGING BY GLUTATHIONE

Enzymatically generated tyrosyl radicals are effectively scavenged by reduced glutathione (GSH), thereby generating glutathione thiyl radica ls and superoxide radicals, subsequently. Here, we have used horseradi sh peroxidase to generate tyrosyl radicals and investigated the fate o f the superoxide radicals, At low GSH concentrations (with a maximum e ffect at 250 mu M) a major reaction was between superoxide and the phe noxyl radical leading to a tyrosine peroxide. Formation of the peroxid e was confirmed using a peroxide-specific colorimetric assay and detec tion of a new HPLC-peak. Its formation was inhibited by superoxide dis mutase (SOD). The peroxide decomposed slowly in a reaction that was ac celerated by GSH to give a new chromatographic peak. Increasing the GS H concentration decreased the amount of tyrosine peroxide formed and c aused increases in rates of oxygen uptake and GSH oxidation. These inc reases were not seen in the presence of SOD and are consistent with GS H scavenging superoxide and leading to oxygen-dependent chain oxidatio n of GSH. Both pathways are undesirable for the cell and are effective ly suppressed only if GSH as a radical scavenger acts in concert with SOD. (C) 1995 Academic Press, Inc.