Oxidative damage of bovine serum albumin and other enzyme proteins by iron-chelate complexes.
Direct oxidative protein damage by iron-nitrilotriacetate (NTA), as well as physiological iron complexes, iron-citrate and iron-ADP was studied in the presence or absence of H2O2, using bovine serum albumin (BSA), glucose-6-phosphate dehydrogenase (G-6-PD), glutathione reductase (GSSGRase) and catalase as the target proteins. Both Fe(III)NTA+H2O2 and Fe(II)NTA+H2O2 caused marked BSA fragmentation which accompanied the decrease in the intrinsic tryptophan fluorescence and appearance of bityrosine fluorescence. However, Fe(III)citrate+H2O2 showed only slight BSA fragmentation. In the absence of H2O2, Fe(II) NTA but not Fe(III)NTA caused similar but slight BSA fragmentation, which depended on the molecular oxygen. Fe(II)citrate also showed O2-dependent BSA fragmentation to a comparable degree, however, Fe(II)ADP showed no detectable BSA damage. BSA fragmentation by Fe(II)NTA+O2 and by Fe(III)NTA+H2O2 resulted in the appearance of the new alpha-amino groups. Electron spin resonance study using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trapping reagent showed DMPO-OH spin adduct, which suggests the presence of hydroxyl radical, in Fe(III)NTA+H2O2, but not in Fe(II)NTA+O2 system. Fe(II)NTA inactivated G-6-PD and GSSGRase in a O2-dependent manner, however, G-6-PD was more susceptible to the damage. This enzyme inactivation also accompanied the protein fragmentation and was not due to simple sulfhydryl oxidation. Catalase was not significantly inactivated nor fragmented by Fe(II)NTA+O2. These findings suggest that the interaction between proteins and iron-chelate complexes is important in iron catalyzed oxidative damage, and that the structure of the chelating agent may determine the target molecules.
Department of Pathology, Okayama University Medical School, Japan.
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Ogino
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Okada
D000818:Animals; D002374:Catalase / Q000378:metabolism*; D002417:Cattle; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism*; D005980:Glutathione Reductase / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000378:metabolism*; D018384:Oxidative Stress; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D019097:Spin Trapping
D003497:Cyclic N-Oxides; D005609:Free Radicals; D007502:Iron Chelating Agents; D012710:Serum Albumin, Bovine; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D005954:Glucosephosphate Dehydrogenase; D002374:Catalase; D005980:Glutathione Reductase