Riboflavin radical generation

They were found not to react with BESOD, the rate constant was estimated to be < 10 M s , if there was a reaction at all The reaction of BESOD was also investigated with several other radicals generated by pulse radiolysis. With the semiquinone of riboflavin 5 -phosphate no reaction was detected. The semiquinone of 9,10-anthraquinone-2-sulfonate and the radical anion of 4-nitroacetophenone converted the enzyme into an unreactive form... 

Neonatal hyperbilirubinemia is normally treated by phototherapy. The peak wavelength for photolysis of bilirubin is 450 nm, the same as that for photolysis of riboflavin (Section 7.1). Infants undergoing phototherapy show biochemical evidence of riboflavin depletion, with a significant increase in the EGR activation coefficient. Provision of additional riboflavin to maintain plasma concentrations enhances the photolysis of bilirubin, apparently as a result of reactive oxygen radicals generated by the products of photolysis of riboflavin. 

Polyacrylamide gels are composed of acrylamide and crosslinking molecule (bisa-crylamide). The polymerization is initiated by the presence of free radicals (generated from ammonium persulfate or other reagents such as riboflavin) and accelerated by a catalyst such as TEMED. The concentration of polyacrylamide gel depends mainly on the size of the analyzed DNA fragment. 

Polyacrylamide gels are made by polymerization of acrylamide (toxic) with N, -methylenebisacrylamide in the presence of free radicals generated from either ammonium persulfate (oxidative chemical initiator) or riboflavin-5 -phosphate (photochemical initiator). The reaction is controlled by equimolar concentrations of N,N,N, N -tetramethylethylene diamine (TEMED) as catalyst. 

One-electron oxidation of the adenine moiety of DNA and 2 -deoxyadenos-ine (dAdo) (45) gives rise to related purine radical cations 46 that may undergo either hydration to generate 8-hydroxy-7,8-dihydroadenyl radicals (47) or deprotonation to give rise to the 6-aminyl radicals 50. The formation of 8-oxo-7,8-dihydro-2 -deoxyadenosine (8-oxodAdo) (48) and 4,6-diamino-5-formamidopyrimidine (FapyAde) (49) is likely explained in terms of oxidation and reduction of 8-hydroxy-7,8-dihydroadenyl precursor radicals 47, respectively [90]. Another modified nucleoside that was found to be generated upon type I mediated one-electron oxidation of 45 by photoexcited riboflavin and menadione is 2 -deoxyinosine (51) [29]. The latter nucleoside is likely to arise from deamination of 6-aminyl radicals (50). Overall, the yield of formation of 8-oxodAdo 48 and FapyAde 49 upon one-electron oxidation of DNA is about 10-fold-lower than that of 8-oxodGuo 44 and FapyGua 43, similar to OH radical mediated reactions [91]. 

Reoxidation of reduced flavin coenzymes is the major source of oxygen radicals in the body, and riboflavin is also capable of generating reactive oxygen species nonenzymically. As protection against this, there is very strict control over the body content of riboflavin. Absorption is limited, and any in excess of requirements is rapidly excreted. 

The scavenging effect of berbamine on active oxygen radicals was studied via a spintrapping technique and a chemiluminescence (CL) method in phorbol myristate acetate (PMA) stimulated polymorphonuclear leukocytes (PMN) and in four-cell superoxide (02+) or hydroxyl radical (OH ) generating systems. The alkaloid (0.1-0.3 mM) effectively reduced active oxygen radicals in PMA-stimulated PMN, but had no obvious effect on oxygen consumption during the respiratory burst of PMN (as measured with spin probe oxymetry). In addition, berbamine (0.3 mM) inhibited the CL response of PMA-stimulated PMN, and quenched 02 in the xanthine/xanthine oxidase and irradiation riboflavin systems, as well as OH in the Fenton... 

The nitroblue tetrazolium assay (111) is another indirect method that is used especially for detecting SOD activity on gel electrophoresis. Superoxide radicals are generated by xanthine/xanthine oxidase or by the photoreduction of flavins (typically riboflavin), which oxidize H2O to O2. The gel on which SOD samples have been loaded is then stained with nitroblue tetrazolium chloride. This reagent is reduced by superoxide to the blue-colored formazan. SOD competes with nitroblue tetrazolium and produces colorless zones on the blue gels. This method, which is highly speciflc toward superoxide dismutase, is limited by its low reliability with respect to quantitative determinations. 

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