title: Structure and catalytic inactivity of the bacterial luciferase neutral flavin radical.
abstract: A luciferase-bound neutral flavin semiquinone radical can be formed upon the oxidation of the luciferase-FMNH2 complex by molecular oxygen. This species can also be formed anaerobically by comproportionation of FMN and FMNH2 in the presence of luciferase. The radical is kinetically stable (t1/2 approximately 20 h at 0 degree C in air; the Arrhenius delta H not equal to decay being about 170 kJ/mol) and can be prepared in pure form by Sephadex G-25 chromatography at 0-4 degrees C. The pure enzyme-bound radical is inactive for light emission either with or without aldehyde, and is not in (relevantly rapid) equilibrium with the luciferase 4a-peroxyflavin, the active intermediate in the bioluminescent reaction.
mesh_terms: D016227:Benzoquinones; D055598:Chemical Phenomena; D002621:Chemistry; D005486:Flavin Mononucleotide / Q000378:metabolism*; D006207:Half-Life; D008156:Luciferases / Q000378:metabolism*; D008163:Luminescent Measurements; D010084:Oxidation-Reduction; D010100:Oxygen; D010545:Peroxides; D011809:Quinones; D013057:Spectrum Analysis; D014733:Vibrio / Q000201:enzymology*; D014737:Vibrionaceae / Q000201:enzymology*
chemical_list: D016227:Benzoquinones; D010545:Peroxides; D011809:Quinones; C025232:semiquinone radicals; D005486:Flavin Mononucleotide; D008156:Luciferases; D010100:Oxygen