ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08877.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—5‐Geranoxypsoralen, commonly called bergamottin, a major furocoumarin contained in bergamot oil, is reportedin vitroas a highly photoreactive psoralen. In ethanol, it exhibits quite a high triplet state quantum yield (≅0.37). The triplet state is involved in subsequent photochemistry which depends on the initial concentration and on the presence of oxygen. In contrast to most psoralens, absorption and fluorescence data suggest that 5‐geranoxypsoralen does not interact with DNA in the dark. No UVA‐induced interstrand cross‐links in DNA

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08461.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The one‐electron reduction and oxidation of 5,10‐methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H0= ‐1 to pH = 7 using the reducing species CO‐2and (CH3)2‐COH and oxidising species Br‐2, and H2SeO+3. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate pK, values of 0.5 ± 0.3 being determined. Both the bridged form (5.10‐methenyltetrahydrofolate) and the unbridged form (5‐ formyltetrahydrofolate) were found to be easily oxidised, whereas only the forme

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08462.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Extraction of a solution of bilirubin configurational isomers in chloroform with an aqueous solution of human serum albumin was found to remove selectively the 4Z, 15E‐isomer. This phenomenon was used to develop a method for the purification of the 4E, 15Z‐isomer of bilirubin. The quantum yield for the cyclization and configurational isomerization of the 4E, 15Z‐isomer bound to a molar excess of human serum albumin was measured at 450 and 510 nm. The quantum yield for cyclization to form lumirubin was 0.12 and 0.19 at 450 and 510 nm respectively. The quantum yield for configurational isomerization to form 4Z, 15Z‐bilirubin was 0.03 and 0.05 at 450 and 510 nm. An analysis of previously published data on the quantum yield for the formation of lumirubin from 4Z, 15Z‐bilirubin bound to human serum albumin suggests that all of the formation of lumirubin may occurviaconsecutive photochemical processes with the 4E, 15Z‐isomer as an

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08463.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Photooxidation, whether initiated by an endogenous or exogenous sensitizer, is an important mechanism in light induced damage to the lens. One of the substrates for this damage is lens protein. A porphyrin sensitizer which binds to lens proteins [mesotetra(p‐sulfonatophenyl) porphyrin (TPPS)] was found to photooxidize Skh‐2 pigmented mice lens proteinin vivo.Uroporphyrin, a model for a non‐binding photosensitizer, did not induce photooxidative damage to the mouse lens.The radioprotector 3‐amino‐2‐hydroxypropyl phosphorothioate (WR‐77913) was investigated as an agent to retard or negatein vivophotooxidative damage to the lens. Intraperitoneal injections of WR‐77913 prior to irradiation reduced the TPPS induced photodestruction of lens protein in Skh‐2 pigmented mice.The mechanism of protection was also investigated. Thiols were found to quench both the triplet state of porphyrins and the reactive intermediate singlet oxygen on the order of 105and 106M‐1s1respectively. These are probably not fast enough to explain most of the protection afforded by thiols. An additional mechanism may be the accelerated photobleaching of porphyrins by thiols which protects tissue by reducing the absorptions

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08464.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The merocyanine 540 (MC540)‐mediated reduction of nitroxide spin labels in a liposomal system was examined using electron spin resonance (ESR) spectroscopy. Spin label reduction was light driven, and occurred in liposomes composed of both fully‐saturated (dimyristoyl) and mono‐unsaturated (1‐palmtoyl‐2‐oleoyl) phosphatidylcholine. Loss of the nitroxide ESR signal was enhanced by the physiological electron donors glutathione, cysteine, and NADPH; and was strongly inhibited by the presence of molecular oxygen. Nitroxides reduced in the presence of MC540 alone could be regenerated either by purging the sample with air or by the addition of ferricyanide, indicating that the ESR signal loss was due to reduction to the corresponding hydroxylamines. Only partial regeneration was attained for nitroxides reduced in the presence of glutathione, cysteine, or NADPH. Reduction rates for the lipophilic spin labels, 5‐, 12‐, and 16‐doxyl stearic acid, were not influenced by the position of the nitroxide moiety along the alkyl chain, however reduction of spin labels occupying primarily the aqueous phase was much slower. These studies demonstrate that MC540 can initiate oxidation/reduction (Type I) reactions. Such Type I processes may augment the effects of singlet oxygen in MC540‐mediated

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08465.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The effect of three purine nucleotides on the fluorescence of methylene blue in aqueous buffer has been investigated. Guanosine‐5′‐monophosphate (GMP) and xanthosine‐5′‐monophosphate cause fluorescence quenching while adenosine‐5′‐monophosphate causes a red shift in the fluorescence maximum. All three nucleotides form ground state complexes with the nucleotides as indicated by absorption spectroscopy. The fluorescence changes at nucleotide concentrations<30 mMare best described by a static mechanism involving the formation of non‐fluorescent binary and ternary complexes in competition with dimerization of the dye. Quenching of the fluorescence decay (τ= 368 ps) at high GMP concentrations (10‐100 mM) occurs at the rate of diffusion. The mechanism of fluorescence quenching may involve electron transfer within the singlet excited dye‐nucleotide complex although published values of the oxidation potentials of various purine derivatives would suggest that all three nucleotides should cause quenching. Evidence for electron transfer was obtained from flash photolysis experiments in which 100 mMGMP was found to cause the appearance of a long lived transient species absorbing in the region expec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08466.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The time‐resolved tryptophyl fluorescence of α‐chymotrypsinogen A and α‐chymotrypsin in the crystalline state and in buffer solution at room temperature was analyzed globally. Tripleexponential decay functions are necessary to adequately describe the tryptophyl fluorescence decay surfaces of the protein powders as a function of hydration and in solution. The fluorescence lifetimes of α‐chymotrypsinogen A (τ1= 0.32 ns. τ2= 1.30 ns. τ3= 3.98 ns) and α‐chymotrypsin (τ1= 0.66 ns. τ2= 2.26 ns. τ3= 5.40 ns) are constant over the entire hydration range. The spectral positions of the decay‐associated spectra of the hydrated powders do not shift as a function of hydration. This indicates that the structures of the zymogen and the active enzyme are unaffected by hydration. The lifetimes of α‐chymotrypsinogen A in phosphate buffer pH 7.4 are τ1= 0.37 ns, τ2= 1.17 ns and τ3= 3.44 ns while the respective values of α‐chymotrypsin are τ1= 0.4

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08467.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—In order to find a photosensitizer with better optical properties and pharmacokinetics than Photofrin II, a series of new photosensitizers related to methyl pheophorbide‐a and chlorin‐e6were synthesized. These compounds absorb at substantially longer wavelengths (Λ max 660 nm) than does Photofrin II (630 nm) and show promise for use in photodynamic therapy. Among the porphyrins, we observed that long carbon chain ether derivatives are better photosensitizers than their ester analogs. These sensitizers were tested forin vivophotosensitizing activity vis‐a‐vis Photofrin II, using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. Most of these photosensitizers were found to have better tumorcidal photosensitizing activity than Photofrin II and demonstrated more rapid attenuation of normal tissue photosensitivity with time after administration vis‐a‐vi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08468.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Site(s) of intracellular localization of a photosensitizing chalcogenapyrylium dye were assessed using murine luekemia cells in culture. While the dye exhibited substantial dark toxicity, additional damage was elicited by irradiation. The fluorescence emission spectrum of intracellular dye suggests an initial moderately hydrophobic site of localization (dielectric constant approx. 20). This might represent a membrane interface. But longer incubations led to alterations in both fluorescence emission and absorbance spectra, indicative of both dye migration to a more hydrophilic cellular site and dye biotransformations. Dye‐induced cytotoxicity, in either light or dark, was associated with mitochondrial, rather than membrane dam

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08469.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY