ABSTRACT
Rational design of hierarchical interfacial assembly of reusable biocatalytic microparticles is described in this chapter. Specifically, purified enzymes and functionalized nanoparticles are electrostatically assembled at the interface of cross-linked microparticles which are formed through ring opening metathesis polymerization. The diameters of microparticle assemblies average 10µm, and they show enhanced kinetic efficiency as well as improved stability against heat, pH, and solvent denaturation when compared to stabilities of the corresponding native enzymes.
Subject(s)
Enzymes, Immobilized/chemistry , Fungal Proteins/chemistry , Lipase/chemistry , Nanoparticles/chemistry , Biocatalysis , Enzyme Stability , Fungal Proteins/isolation & purification , Hydrogen-Ion Concentration , Kinetics , Lipase/isolation & purification , Polymerization , Protein Denaturation , Solvents/chemistryABSTRACT
The xanthone-sensitized photodecomposition of the fatty ester hydroperoxides 1 and 2 in the presence of pBR 322 DNA was investigated as a chemical model system to assess whether this process may cause DNA damage through oxyl radicals. Unequivocally, oxyl radicals are formed in the xanthone-sensitized photodecomposition of the hydroperoxides 1 and 2, as confirmed by EPR studies. Indeed, both hydroperoxides 1 and 2 induce DNA single-strand breaks upon uv-A irradiation in the presence of the exogenous sensitizer xanthone. Under similar reaction conditions, the corresponding alcohol 3 of the hydroperoxide 1 was ineffective. Mannitol as radical scavenger inhibited significantly the formation of DNA single-strand breaks in the xanthone-sensitized decomposition of the hydroperoxides 1 and 2. Irradiation of xanthone alone or the hydroperoxides 1 and 2 without sensitizer did not cause any detectable DNA single-strand breaks. These results confirm that photosensitization of the fatty ester hydroperoxides 1 and 2 induces DNA modifications by oxyl radicals. We suspect that the combination of endogenous photosensitizers, solar uv radiation, and lipid hydroperoxides may damage cellular DNA through oxyl radicals.
Subject(s)
Lipid Peroxides/chemistry , Oleic Acids/chemistry , Peroxides/chemistry , Plasmids/chemistry , Ultraviolet Rays , Cyclic N-Oxides , DNA Damage , Electron Spin Resonance Spectroscopy , Lipid Peroxides/radiation effects , Oleic Acids/radiation effects , Peroxides/radiation effects , Photochemistry , Plasmids/radiation effects , Spin Labels , XanthinesSubject(s)
DNA Damage , DNA/drug effects , Heterocyclic Compounds/pharmacology , Hydrogen Peroxide/pharmacology , Iron/pharmacology , Ketones/pharmacology , Lipid Peroxides/pharmacology , Mutagens/pharmacology , Photosensitizing Agents/pharmacology , Animals , Cattle , DNA/chemistry , Guanine/analogs & derivatives , Guanine/analysis , Heterocyclic Compounds, 1-Ring , Oxazolone/analysis , Oxidation-ReductionABSTRACT
Xanthone-sensitized photo-oxidation of guanine in calf thymus DNA and in the nucleoside 2'-deoxyguanosine has been investigated in the presence of various additives, with major emphasis on hydroperoxides. The formation of the guanine oxidation products 7,8-dihydro-8-oxoguanine (8-oxoGua), which is a marker for oxidative DNA damage, and 2,2-diamino-4-[(2-deoxy-beta-D-erythro-pentofuranosyl)amino]-5(2H)-oxazo lone (oxazolone) was monitored quantitatively by high performance liquid chromatography electrochemical or fluorescence analysis. Irradiation (350 nm) of calf thymus DNA in the presence of xanthone as sensitizer afforded 8-oxoGua in 1.4% yield. The ethyl oleate hydroperoxide 1a and its alcohol 1b inhibit the formation of 8-oxoGua very efficiently (up to 85%). Even the structurally simple t-butyl hydroperoxide and the physiologically relevant hydrogen peroxide exhibit strong inhibition of photosensitized oxidation of guanine in DNA and in the nucleoside, while t-butanol and the allylic alcohols 3b and 4 do not. Hydroperoxides in general quench type I-sensitized (benzophenone, xanthone) photo-oxidation of guanine, but not that of rose bengal, a predominant type II sensitizer. The inhibiting effect is explained by H abstraction of the electronically excited carbonyl chromophore from the additive. The biological relevance of these findings should be seen in the potential protecting role of lipid hydroperoxides and their corresponding alcohols against oxidative stress.