Reactions of oxidizing and reducing radical probes with lipoamide dehydrogenase.
One-electron redox radicals generated by radiation--chemical methods have been reacted with the oxidized (E) form of pig heart lipoamide dehydrogenase. The reducing radicals eaq- and CO2-. and O2-. do not measurably inactivate the enzyme, whereas the oxidizing species .OH and Br2-. do. The CO2-. anion forms the semiquinone radical .EH on the millisecond time scale, whereas at longer times only EH2 is observed. Evidence suggests that Br2-. oxidizes adjacent sulfhydryl groups to form a disulfide in a manner similar to the reaction of Cu2+ ions. With .OH, destruction of the flavin adenine dinucleotide (FAD) moiety is responsible for at least 50% of the enzyme inactivation. This destruction appears to be a result of secondary reactions which transfer damage from remote initial sites of attack to the flavin. Pathways for migration of eaq- damage also appear to exist.
D001965:Bromides; D002245:Carbon Dioxide; D055598:Chemical Phenomena; D002621:Chemistry; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors / Q000528:radiation effects*; D005182:Flavin-Adenine Dinucleotide / Q000528:radiation effects; D005609:Free Radicals; D005720:Gamma Rays; D010084:Oxidation-Reduction; D010100:Oxygen; D013053:Spectrophotometry
D001965:Bromides; D005609:Free Radicals; D002245:Carbon Dioxide; D005182:Flavin-Adenine Dinucleotide; D008058:Dihydrolipoamide Dehydrogenase; D010100:Oxygen