Reactions of lumiflavin with amine radicals

Abstract

The amino radicals (.AH) formed by the h°Co radiolysis of N,O-saturated 0.05 M solutions of ethylene diamine tetraacetate (EDTA) at pH 7 and 11.2 and of glycine at pH 11.2 brought about an efficient two-electron reduction of lumiflavin (FI). The spectra of the products were identical to those formed by photolysis of the same solutions and by reduction of the lumiflavin with .CO,-radicals. The products were reoxidised to flavin by oxygen. The quantum yield for flavin disappearance was 0.52 2 0.07 and 0.17 ? 0.01 in the presence of EDTA at pH 7 and 1 1.2 and 0.065 + 0.008 and 0.17 ? 0.01 for glycine at the same pHs, respectively.The overall two-electron reduction can be explained by the mechanism:The rate constants of reaction [4] were found by pulse radiolysis to be 1.8 ? 0.3 x 10' and 1.5 ? 0.3 X 10" M-' s-' for the radicals of glycine and EDTA at pH 7 and 3.6 * 0.3 x 1 0 H M S -I for glycine radicals at pH 11.2. The spectrum of .FIH formed by glycine radicals at pH 7 is similar to that produced by .CO,-, but there was some perturbation, which is apparently due to interaction with the amine. The radicals formed from the secondary amines piperazine and diethylamine at pH I 1.8 also effected reversible two-electron reduction. However, the radicals from glycine anhydride and the primary amine ethylamine yielded significant amounts of non-oxidisable products. The reaction mechanisms are discussed and effects of pH are considered. PARMINDER S . SURDHAR, DOUGLAS E. BADER et DAVID A. ARMSTRONG. Can. J. Chem. 63, 1357 (1985). Les radicaux arninks (.AH) issus de la radiolyse au "Co de solutions saturkes en N,O, contenant 0,05 M de tetraacktate d'kthylene diamine (TAED) at maintenues a des pH de 7 ou 11,2 ou contenant de la glycine a un pH 11,2, provoquent une rkduction deux Clectrons efficace de la lumiflavine (FI). Les spectres des produits sont identiques a ceux des produits obtenus par la photolyse des mCmes solutions et par la reduction de la lumiflavine par les radicaux .CO,-. L'oxygkne provoque une rkoxydation des produits en flavine. A des pH de 7 et 11,2 et en presence du TAED, les rendements quantiques pour la disparition de la flavine sont respectivement kgaux a 0,52 2 0,07 et de 0,17 ? 0,01 alors qu'en presence de glycine et aux mCmes pH ces rendements sont Cgaux a 0,065 2 0,008 et 0.17 ? 0,Ol.On peut ilustrer la reduction globale a deux Clectrons, par le mecanisme suivant:Faisant appel a la radiolyse pulsation, on a pu Ctablir que les constantes de vitesse de la reaction [4] sont Cgales a 1,8 2 0,3

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO2 and dithiothreitol

“…3(a). This type of behaviour has been seen in reactions of e&, and certain amine radicals with lumiflavin (15,19). It is attributed to a further and irreversible reduction of HH2 by these species.…”

Reactions of α-carbon- and nitrogen-centered radicals of piperazine with lumiflavin and paranitroacetophenone at pH 7

“…In the first place amine (AH2) molecules can be used as hydrogen donors to convert flavins (Fl) to their dihydro forms (1)(2)(3)(4) through the reaction sequence: [ I ] F I + h v +~l~+~l ' [2] AH2 + F I~+ 'AH + 'FIH [3] 'AH + 'F1H + A + FIHz…”

“…It was pointed out in ref. 4 that further progress required a knowledge of the proportions of nitrogen-centered (viz. : '~3 ) and carbon-centered radicals / (viz.…”

“…4 two studies which are very relevant to the above question have been published. In the first place Monig et al (6) have shown that deprotonated a-amino acids have a high tendency to form a-carbon-centered radicals, which are strongly reducing.…”

“…Their work provided evidence for three radical forms, would lead to enzyme inactivation. Studies of these reactions which were related by the protonation-deprotonation equilibria thus have a bearing on our understanding of important biobelow: logical processes and the pharmacology related to them (4).…”