SIMULTANEOUS GROWTH AND DECAY OF FREE RADICALS IN IRRADIATED PROTEINS

Abstract— The electron paramagnetic resonance signals due to free radicals created in illuminated keratin have been studied during illumination and also during the decay of the signal in the dark. A number of mechanisms suggested to account for the simultaneous growth and decay of radicals during illumination is considered but only one of these is capable of accounting for the experimental results.     

DETERMINATION OF INTRINSIC CONSTANTS FOR THE KINETICS OF GROWTH AND DECAY OF FREE RADICALS IN ILLUMINATED KERATIN

Abstract— The growth and the decay of free radicals in illuminated keratin of five samples of wool have been studied by electron paramagnetic resonance. Illumination of the different samples varied from 10^-9 to 10^-7 Einstein cm^-2s^-1. The paramagnetic resonance spectra were measured both during illumination and during the decay of signals in the dark. The curves obtained during illumination gave two typical shapes: one approaching the apparent "saturation value", and the other passing through a maximum and then decreasing despite continuing illumination. All the above results are discussed in terms of only two prevalent free-radical species, whose growth and decay are determined for each species by a single intrinsic growth constant, and a single intrinsic decay constant. These four constants allow a reasonable fit for the complete behaviour of all five samples.     

ESR STUDY OF FREE RADICALS IN IRRADIATED POLYAMIDE-1010

Polyamide-1010 samples were irradiated in vacuum at room temperature by Cobalt-60 γ-rays. The free radicals formed in irradiation were studied by means of electron spin resonance (ESR)techniques.The ESRspectra consisted of a quartet and a superimposed singlet which were attributed to radical -CO-NH-CH-CH_2 and -CH_2-C=O, respectively. The effects of temperature and crystaUinity on the radicals were discussed and the mechanism for the production and decay of the radicals was also proposed.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.     

FREE RADICALS DETECTED BY ESR FROM PHENYLHEPTATRIYNE IN LIPOSOMES IRRADIATED WITH UV-A

Abstract— When irradiated with UV-A liposome bilayers composed of distearoyl phosphatidylcholine and containing phenylheptatriyne produced a free radical signal detected by electron spin resonance spectroscopy. The spectrum contained one broad peak characterized by a linewidth of 19 G and a g value of 2.0017. The rate of formation of the signal amplitude was dependent upon light intensity, concentration of PHT within the bilayer and concentration of the PHT-liposome suspension. Enhancement of the signal under an anaerobic atmosphere indicated a non-photodynamic mechanism for free radical formation. Once formed however, the free radical was stable to the presence of oxygen and decayed very slowly with a half-life of 8 h. Formation of the free radical species was demonstrated to be dependent upon a highly ordered lipid environment since incorporation of lysophosphatidylcholine, stearoyl which perturbs lipid packing, decreased the levels of the free radical species. On the other hand, when PHT was present in a liposome with a more fluid bilayer such as egg yolk phosphatidylcholine, the levels of free radical species were even lower. Conversely, the levels increased when cholesterol which increases lipid order, was incorporated into the egg yolk phosphatidylcholine liposomes. Cells of E. coli, B , containing PHT, produced a similar free radical signal upon irradiation demonstrating in vivo generation of free radicals from PHT.     

烟草中自由基的研究进展

自由基是卷烟烟气中主要的一类有害物质，能导致人体组织和细胞的氧化，损害细胞膜上的脂类和蛋白质。引发癌症等疾病。对烟草中自由基的研究情况、自由基的检测方法、降低卷烟中自由基含量的研究等方面进行了综述。     

DISTRIBUTIONS OF FREE RADICALS AMONG AMINO ACIDS FROM LYOPHILIZED ULTRAVIOLET-IRRADIATED PROTEINS

Abstract— The effects of u.v.-irradiation at 254 nm upon lyophilized ribonuclease, lysozyme, insulin, and chymotrypsinogen have been investigated by electron spin resonance (ESR). enzymatic assay, and labeling of free radical sites with tritiated hydrogen sulfide (HST). The ESR signal of the irradiated protein diminishes on exposure to HST, and tritium becomes covalently bound to carbon. The distribution of tritium among the amino acids of each protein. studied as an indicator of the carbon free radical distribution, differs markedly from those observed previously to result from exposure to gamma radiation, electrical discharge. or hydrogen atoms. However, the earlier observation that the tritium distribution is influenced by protein conformation holds true as well for u.v.-irradiation. Moreover, the distributions of tritium among the amino acids of u.v.-irradiated proteins indicate a broad scattering of free radicals. Tyrosine and phenylalanine, residues that absorb light energy in the region of the wavelength employed, are not particularly important as radical carriers. Thus, for ribonuclease, these residues incorporated 3.8 and 1.5 per cent of the total tritium, but they absorb 51 and 12 per cent of the light, respectively. These results, together with the observed low recoveries of methionine, an amino acid that does not absorb at 254 nm, add weight to the concept that a migration of energy ensues after the initial absorption of light energy and that photolytic damage may thus be due to destruction of amino acids other than those initially absorbing the u.v.-radiation.     

香烟烟雾中自由基的检测

对香烟焦油中的Q/H2Q自由基及气相中的自由基进行了测定，同时对香烟燃烧产生自由基的机理进行了探讨。     

FREE RADICALS FROM PHOTOREDUCTION OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

—The anaerobic photoreduction of hematoporphyrin by organic reducing agents in fluid aqueous solutions has been studied by electron spin resonance spectroscopy. Efficient photoreduction occurs with many hydrogen-atom or electron donors, including catechols, pyrogallol. hydroquinone. ascorbate, p -phenylenediamine, cysteine and glutathione. A combination of direct and spin-trapping measurements (using 2-methyl-2-nitrosopropane) has been used to confirm production of radicals from both the porphyrin and the reducing agent in each system.     

FREE RADICALS FROM PHOTODECOMPOSITION OF BISPHENOL-A

Abstract— Irradiation of 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol-A) with UV light causes photo-decomposition of the compound. Spin-trapping with α-phenyl-N-tert-butyl-nitrone showed that free radicals were cleaved from the molecule. No direct ESR-spectroscopic information concerning the structure of the remaining radical skeleton could be obtained. Gas chromatographic mass spectrometric analysis of the decomposition products indicated the existence of a semiquinone structure following cleavage of a methyl radical from 2,2-bis-4–(hydroxyphenyl)-propane. The capacity of 2,2-bis-(4- hydroxyphenyl)-propane to give rise to radicals might explain its photoallergenic properties.     

ELECTRON SPIN RESONANCE OF TRIPLET STATES AND FREE RADICALS APPEARING IN PORPHYRINS, AROMATIC AMINO-ACIDS AND PROTEINS UNDER THE EFFECT OF LIGHT

Abstract— The electron paramagnetic resonance (EPR) of the triplet excited state of solutions of a series of porphyrins and aromatic amino-acids has been studied at 77°K. It has been shown that for some of the compounds it is possible to observe EPR for transitions with δ M =±1, ±2.
It has been shown that photoreactions in solid solutions of porphyrins and aromatic amino-acids proceed through the triplet excited state.
Reactions of photosensitized deamination of aliphatic amino-acids in solid aqueous solutions at 77°K by aromatic compounds have been studied.     

细菌视紫红质-聚乙烯醇薄膜M态衰减动力学研究

利用闪光光解法和紫外 可见光谱法研究了室温条件下,pH值的增加和干燥时间的延长对细菌视紫红质 (bR)-聚乙烯醇 (PVA)薄膜光循环过程中M态衰减动力学的影响。闪光光解动力学研究表明,M态的衰减随着 pH值的提高和干燥时间的延长而明显减慢,在pH =1 0和干燥时间为 72h的最佳制备条件下薄膜M态的衰减最为缓慢.紫外 可见光谱法表明,M态的衰减可持续 15min以上,比自然条件下M态的寿命提高约 4个数量级.本文还探讨了最佳制备条件下细菌视紫红质-聚乙烯醇薄膜长寿命M态形成的机理.     

LIGHT-INDUCED FREE RADICALS IN ORIENTED DNA-PROFLAVINE COMPLEXES

Abstract— Oriented wet DNA-proflavine complexes were illuminated with visible light, Λ > 395 nm, at 77 K, in the presence or absence of oxygen. The electron paramagnetic resonance spectra at 77 K and low microwave power (3 μ W) indicated formation of anionic free radicals in thymine and cationic free radicals, probably in guanine, identical to those induced by y rays at 77 K in similar samples of pure DNA.
The free-radical formation rate showed a quadratic dependence on light intensity, indicating a biphotonic mechanism. The proflavine triplet spectrum was observed during illumination. If the exciting light includes wavelengths below 390 nm, significant amounts of hydrogen addition radicals in thymine are found.     

EPR PERSISTENCE MEASUREMENTS OF UV-INDUCED MELANIN FREE RADICALS IN WHOLE SKIN

Electron paramagnetic resonance is used to detect the formation of free radicals caused by exposure to ultraviolet radiation in chemically untreated rabbit skin. A fast jump in EPR signal level, occurring over a few seconds, is observed immediately after a skin sample is exposed to UV. This is followed by a slower increase toward an elevated steady-state signal over a period of hours as the skin is continuously exposed to a UV light source. Upon cessation of UV light exposure, EPR signal levels undergo an abrupt drop followed by a slower decay toward natural levels. Elevated free radical concentrations following UV exposure are found to persist for several hours in whole skin. These results are consistent with time-resolved EPR measurements of photoinduced radicals in various natural melanins.     

FLUORESCENCE DECAY KINETICS and CHARACTERISTICS OF BIMOLECULAR EXCITON ANNIHILATION IN CHLOROPLASTS

Abstract— The decay profiles of the fluorescence of dark-adapted spinach chloroplasts (0^A°C) excited with single 30 ps 532 nm laser pulses of varying intensities were measured with a low-jitter streak camera system. By comparing the decay profiles of the fluorescence at low and high laser fluences, i.e. in the absence and presence, respectively, of dynamic bimolecular exciton-exciton annihilation effects, the duration of such dynamic annihilation events can be estimated. A simple model suggests that the influence of bimolecular annihilation events on the fluorescence decay kinetics should disappear within a time interval corresponding to the low intensity, unimolecular lifetime of the exciton population which is subject to exciton-exciton annihilation. The low intensity fluorescence decay profiles are characterized by three to four lifetimes (Reviewed by A. R. Holzwarth, Photochem. Photobiol. 43,707–725, 1986); it is shown here that only the shortest fluorescence components are subject to exciton annihilation, since the kinetics of the fluorescence decay are influenced by annihilations only within the initial 150–200 ps time interval after the excitation pulse. The amplitudes (but not the decay kinetics) of the longer-lived fluorescence components are decreased at high levels of laser pulse excitations, suggesting that these components are derived from the shorter-lived fluorescence decay components. The implications of these results are*discussed within the contexts of current models of the fluorescence in chloroplasts.     

FREE RADICALS FROM THE PHOTODECOMPOSITION OF BLEOMYCIN

Abstract— Irradiation of bleomycin with light (λ > 320 nm) leads to a decrease in absorbance at 290 nm, which is suppressed by metal ions and by oxygen. Light-induced oxygen consumption is diminished by the enzymes superoxide dismutase and catalase, implying that toxic reduced species of oxygen (O₂ and H₂O₂) are formed during irradiation. Spin-trapping measurements with 5,5-dimethyl-1-pyrroline-1-oxide and 2-methyl-2-nitrosopropane demonstrated that hydroxyl radical and methyl radical adducts also are generated in the system. In addition, direct ESR measurements have shown that methyl radicals are produced during irradiation of bleomycin solutions at low temperatures, together with radicals probably derived from the bithiazole moiety of the bleomycin. The latter are also produced from irradiation of the model compound bithia. Radical production is diminished by complexation of bleomycin with metal ions.     

THE FORMATION OF FREE RADICALS AND THE CONSEQUENCES OF THEIR REACTIONS IN VIVO

Abstract— Mechanisms for the initiation of free radical reactions in vivo are reviewed, including ozone and ¹O₂ reactions, radiation, one-electron transfer processes, and enzymatic reactions. The roles that radical reactions might play in aging processes and in carcinogenesis are discussed.     

DECAY KINETICS OF THE TRIPLET EXCITED STATE OF LUMIFLAVIN

Abstract— The rate of decay of the triplet state of lumiflavin in deaerated phosphate buffer at pH 6.9, has been studied using the flash photolysis technique, at various concentrations and flash energies. The decay of the transient appears as a mixture of first and second order processes, the relative importance of which depends on the experimental conditions.
The following competitive reactions have been found to explain the course of the reaction of the triplet excited state of lumiflavin.     

水杨醛缩对甲苯胺的吸收光谱和失活动力学研究

利用纳秒级的闪光光解方法研究了水杨醛缩对甲苯胺的瞬态吸收光谱。根据瞬态吸收光谱和动力学数据,该化合物的基本光产物被认为是一个两性离子。实验结果表明,光产物的性质与溶剂的性质和浓度有关。对该化合物的光致变色机理也进行了讨论。     

用电子自旋共振谱研究我国一些煤的自由基

本文用电子自旋共振谱(ESR)研究了我国十种不同变质程度的煤。电子自旋共振最重要的参数是g值、自由基的浓度、线宽和线形。用这些参数与煤中的碳、氧等元素相关联,发现ESR参数与煤的变质程度有密切关系。