The role of reactive N-bromo species and radical intermediates in hypobromous acid-induced protein oxidation.
Activated eosinophils, and hypobromous acid (HOBr) generated by these cells, have been implicated in the tissue injury in asthma, allergic reactions, and some infections. Proteins are major targets for this oxidant, but limited information is available on the mechanisms of damage and intermediates formed. Reaction of HOBr with proteins is shown to result in the formation of bromamines and bromamides, from side-chain and backbone amines and amides, and 3-bromo- and 3,5-dibromo-Tyr, from Tyr residues; these materials account for ca. 70% of the oxidant consumed. Protein carbonyls, dityrosine, and 3,4-dihydroxyphenylalanine are also formed, though these are minor products (<5% of HOBr added). With BSA, extensive (selective and nonspecific) protein fragmentation and limited aggregation are also observed. The bromamines/bromamides are unstable and induce further oxidation and free radical formation as detected by EPR spin trapping. Evidence was obtained for the generation of nitrogen-centered radicals on side-chain and backbone amide groups of amino acids, peptides, and proteins. These radicals readily undergo rearrangement reactions to give carbon-centered radicals. With proteins, alpha-carbon (backbone) radicals are detected, which may play a role in protein fragmentation. A novel damage transfer pathway from Gln side-chain amide groups to backbone sites was also observed.
Hawkins
Clare L
CL
The Heart Research Institute, 145 Missenden Road, Camperdown, Sydney, NSW 2050, Australia.
Davies
Michael J
MJ
D000577:Amides / Q000138:chemical synthesis; D001959:Bromates / Q000737:chemistry*; D001965:Bromides / Q000138:chemical synthesis*; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004591:Electrophoresis, Polyacrylamide Gel; D005609:Free Radicals / Q000378:metabolism*; D007328:Insulin / Q000737:chemistry; D009113:Muramidase / Q000737:chemistry; D010084:Oxidation-Reduction; D020836:Protein Structure, Quaternary; D011506:Proteins / Q000737:chemistry* / Q000187:drug effects*; D012259:Ribonuclease, Pancreatic / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry; D013113:Spin Labels; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000737:chemistry; D014443:Tyrosine / Q000031:analogs & derivatives / Q000138:chemical synthesis
D000577:Amides; D001959:Bromates; D001965:Bromides; D003497:Cyclic N-Oxides; D005609:Free Radicals; D007328:Insulin; D011506:Proteins; D013113:Spin Labels; C475724:bromotyrosine; C032714:bromamine; C098505:5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide; D012710:Serum Albumin, Bovine; D014443:Tyrosine; D014360:Trypsin Inhibitor, Kunitz Soybean; D012259:Ribonuclease, Pancreatic; D009113:Muramidase; C027664:hypobromous acid