Flavins oxygen complexes

Anderson, R. F. Flavin-oxygen complex formed on the reaction of superoxide ions with flavo-semiquinone radicals. In Flavins and flavoproteins (Massey, V., Williams, C. H. eds.) pp. 278-283, New York, Elsevier North Holland 1982... 

It was suggested that the reduced flavins yield a flavin-oxygen complex called HFIOOH which may exist in two isomeric forms (Fig. 25). Either of these intermediate compounds can follow the different decay modes depicted in Fig. 25. Only the intermediate type V yields the... 

As in the case of the reduced flavin-oxygen complex HFIOOH, where any of a number of possible intermediates are being formed... 

R. F. Anderson, Flavin-Oxygen Complex Formed on the Reaction of Superoxide Ions with Flavosemiquinone Radicals. In Flavins and Fiavoproteins) V. Massey, C. H. Williams, Eds. Elsevier North-Holland New York, 1982 pp 278-283. 

After some remarks on flavoquinone the structural discussion of possible reaction intermediates will start with the radical (= complex ofFlox + e ) and continue with dihydroflavin (= complex ofFlox + H"), flavin-substrate complexes (Flox + R") and flavin-oxygen complexes (Flox + OOH ). Scheme 6 illustrates the a-input and -output positions for formation and decay of these intermediates. 

Scheme 13. Formation of Blue Flavin-Oxygen Complex Bz = benzoyl. The overall reaction is 2CH3Fl,edH + Bz202 + 02 (CH3FI-O-F+ 2 BzOH. The known blue alloxane-...

The deprotonated flavin in the complex is readily attacked by molecular oxygen at C4a, giving 4a-hydroperoxide of the flavin-luciferase complex (intermediate A). This complex is an unusually stable intermediate, with a lifetime of tens of seconds at 20°C and hours at subzero temperatures, allowing its isolation and characterization (Hastings et al., 1973 Tu, 1979 Balny and Hastings, 1975 Vervoort et al., 1986 Kurfuerst et al., 1987 Lee et al., 1988). 

Tu, S.-C. (1979). Isolation and properties of bacterial luciferase-oxygenated flavin intermediate complexed with long-chain alcohols. Biochemistry 18 5940-5945. 

Chemiluminescence has been observed during the oxidation of these compounds by molecular oxygen in the presence of heavy metal catalysts. Copper-II-compounds ([Cu (NH3)4] + and a Cu- flavin mononucleotide complex) were found to be especially efficient. The emitting species seems to be singlet oxygen in both cases. The emission is accompanied by FMN fluorescence [52]. 

A still more complicated reaction is the chemiluminescent oxidation of sodium hydrogen sulfide, cysteine, and gluthathione by oxygen in the presence of heavy metal catalysts, especially copper ions 60>. When copper is used in the form of the tetrammin complex Cu(NH3) +, the chemiluminescence is due to excited-singlet oxygen when the catalyst is copper flavin mononucleotide (Cu—FMN), additional emission occurs from excited flavin mononucleotide. From absorption spectroscopic measurements J. Stauff and F. Nimmerfall60> concluded that the first reaction step consists in the addition of oxygen to the copper complex ... 

Thus, step 1 involves addition of NADPH and reduction of the flavin, step 2 the addition of oxygen. At step 3, an internal rearrangement results in the formation of a peroxy complex, which then binds the substrate at step 4. The substrate is oxygenated and released at step 5. 

---