Photochemistry of protein and nucleic acid constituents: electron spin resonance and spin-trapping with 2-methyl-2-nitrosopropane

Abstract

PETER RIESZ and IONEL ROSENTHAL. Can. J. Chem. 60, 1474Chem. 60, (1982. Our recent studies of the direct uv-photolysis of aliphaticand aromatic peptides, DNA constituents, and their 5-haloderivatives in aqueous solution and the photo-induced reactions of benzoylperoxide with amino acids, peptides, fatty acids, and pyrimidines in dimethylsulfoxide-containing solutions are reviewed.2-Methyl-2-nitrosopropane was used for spin-trapping and characterization of free radicals generated photochemically with light in the wavelength range of220-313 nm in aqueous oraprotic solvents. Direct photolysis of aliphatic dipeptides and of phenylalanine peptides produced mostly decarboxylation radicals, while for tyrosine peptides both decarboxylation and deamination radicals were spin-trapped; for tryptophan di-and tripeptides, deamination radicals were predominantly produced, while for long chain polypeptides, main-chain scission was observed.When pyrimidine bases were photolysed, radicals consistent with the addition of an H-atom or an OH-radical at the C(5) position of the 5,Gdouble bond could be detected. The general reaction pattern in the photolyses of 5-chloro, bromo, or iodouracil was the homolytic cleavage of the carbon-halogen bond, while for 5-fluorouracil, the a-fluoro radical was spin-trapped.Dibenzoylperoxide was found to photoinduce the free radical generation in amino acids, peptides, and fatty acids exposed to ultraviolet light, which is not absorbed by these compounds, that is, h = 313 + 10 nm. The most predominant reaction is the decarboxylation of the terminal acid moiety. This process is explained by an electron transfer from the acid to the photoexcited peroxide or its fragmentation products. Pyrimidine bases, such as cytosine and thymine, can be oxidized under these conditions to generate C(5) centered radicals.PETER RIESZ et IONEL ROSENTHAL. Can. J. Chem. 60, 1474Chem. 60, (1982. On passe en revue nos rtcentes Ctudes sur la photolyse direct uv des peptides aromatiques et aliphatiques, des constituants de I'ADN et de leurs dCrivts halogenCs en solution aqueuse ainsi que les riactions photo-induites du peroxyde de benzoyle avec les acides aminks, les peptides, les acides gras et les pyrimidines dans des solutions contenant du dimethylsulfoxyde.Nous avons utilist le methyl-2 nitroso-2 propane comme capteur de spin et pour caracttriser les radicaux libres produits photochimiquement avec une lumiere dont la longueur d'onde vane de 220 a 313 nm dans des solvants aqueux ou aprotiques. La photolyse directe des dipeptides aliphatiques et des peptides contenant de la phCnylalanine produit surtout des radicaux de dtcarboxylation, tandis que dans les cas des peptides contenant la tyrosine, on a captC des radicaux de dtcarboxylation et de dtsamination. Dans le cas des di-et des tripeptides du tryptophane, on obtient surtout des radicaux de dtsamination tandis que I'on observe une scission de la chaine principale dans le cas des longues chaines de polypeptides.Quant on photolyse les bases du type pyrimidine, on dttec...

PHOTOGENERATION OF SUPEROXIDE and DECARBOXYLATED PEPTIDE RADICALS BY CARBOQUONE, MITOMYCIN C and STREPTONIGRIN. AN ELECTRON SPIN RESONANCE and SPIN TRAPPING STUDY

“…The ESR spectra in Fig. 3 also contain an overlapping triplet (labeled S) originating from ditertiary butyl nitroxide (d-tBN) formed in the photolysis of MNP (Riesz and Rosenthal, 1982). Figure 3a shows the ESR spectrum of the MNP spin adduct of decarboxylated alanylglycine.…”

Generation of Free Radicals During Photosensitization of Hypocrellin a and Their Effects on Cardiac Membranes

“…The mechanism by which they are damaged during exposure to HA is not well understood. Most photosensitizers when exposed to light can be activated, and in the presence of oxygen can produce reactive species such as singlet oxygen (lo2), superoxide anion (03, hydroxyl radical (.OH) and various other free radicals, all of which can damage biological molecules of cells (Riesz and Rosenthal, 1982;Zhang et al, 1986). Electron paramagnetic resonance (EPR) provides an effective way for detecting the initial transient radical species (Mossoba et al, 1984).…”

Oxidative degradation of collagen and its model peptide by ultraviolet irradiation

“…However, the effect of ultraviolet irradiation on protein components in food was unknown in detail, although that of -irradiation on protein was examined by many workers. Previously, photolysis of peptides was investigated using ESR (Lion et al, 1980; Riesz and Rosenthal, 1981; Sevilla and D'Arcy, 1978), flash photolysis (Mittal et al, 1973), and chemical product analysis (Hill et al, 1991). Photooxidation of aliphatic amino acids and peptides was found to lead primarily to photoinduced decarboxylation (Mittal et al, 1973).…”