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1.
SALT AND pH-DEPENDENT CHANGES OF THE PURPLE MEMBRANE ABSORPTION SPECTRUM 总被引:19,自引:0,他引:19
Yoshiaki Kimura Akira Ikegami Walther Stoeckenius† 《Photochemistry and photobiology》1984,40(5):641-646
Abstract —Purple membrane suspensions change their color to blue and the absorption maximum shifts to 608 nm when the membrane is deionized on a cation exchange column or when it is washed first with < 2N NaCl followed by deionized water. The deionized chromophore is essentially identical with the chromophore produced by lowering the pH of the native membrane to < 4.0 (p K < 3.0). However, the deionized membrane does not aggregate and can be obtained in the pure state. The original purple color of the membrane is restored by addition of around 1 m M Na+ , K+ or 10 μ M Mg2+ , Ca2+ , Sr2+ , Mn2+ , Pb2+ or La2+ when the protein concentration is 5μ M . The required salt concentrations decrease with decreasing pH. Direct measurement of bound Ca2+ by atomic absorption spectroscopy yields a ratio of Ca2+ to protein of <2 and a binding constant of 1.4 × 106 . Titration of the spectral change with salts at different pH values shows a linear relation between the pH and the logarithm of the salt concentration, with a 1:1 ratio for Na+ and 1:2 ratio for Ca2+ . These relations are well predicted by Gouy-Chapman theory; however, the accompanying release of protons, changes of the CD spectrum, the complex kinetics of the spectral change during reconstitution with salt and preliminary X-ray diffraction results all suggest that conformational changes may be occurring in the protein. 相似文献
2.
Abstract— The photooxidation of reduced lumiflavin in its acidic form, LfH 3 + , takes place in two consecutive steps. Upon illumination of LfH 3 + in its absorption band at 313 nm the semiquinone, LfH 3 + , is formed. Two LfH 2 + ions are consumed for every LfH 2 + formed. Illumination of the semiquinone in its absorption band at 495 nm causes further oxidation so that the oxidized LfH+ ion is formed. In this reaction one LfH 3 + ion is photolyzed for every LfH+ formed. In addition, a hydrogen atom is released in the photooxidation of LfH 2 + . Mechanisms for the two photoreactions are proposed. 相似文献
3.
Thaddeus Prusik Tatiana Kolubayev Michael J. Morelli Henry C. Brenner 《Photochemistry and photobiology》1980,31(4):315-321
Abstract— The luminescence of acridine dyes intercalated in DNA was studied as a function of the concurrent binding of metal ions to DNA, in an effort to deduce specific site interactions of the dyes. Two dyes, proflavine (PF) and acridine orange (AO), and two metal ions, silver and mercuric, were used. Both ions quench the fluorescence of the dyes in aqueous solution at room temperature. The metal ions have a different effect on the fluorescence of these dyes when they are intercalated between the base pairs of DNA. The fluorescence of AO is decreased when silver is bound, while the fluorescence of PF is enhanced. Since Ag+ initially binds to GC sites in DNA, which quench the PF fluorescence, it ostensibly 'turns off' the quenching by DNA at these sites, and this effect is greater than the quenching effect of the silver ion itself. Hg2+ ion initially binds to AT sites in DNA. Since both dyes fluoresce from AT sites, Hg2 + is expected to quench their fluorescence. This behavior is observed at low r (metal ion/base). At higher r values, however, where Hg2 + is expected to begin binding to GC sites, the fluorescence of PF is enhanced. These quenching turn-off effects are tentatively interpreted in terms of a change in the structure of the dye/DNA complex which occurs when a metal ion binds at the intercalation site. At 77 K. no fluorescence enhancement is observed when metal ions bind; Ag+ quenches the fluorescence and enhances the phosphorescence of both dyes. Qualitatively similar results are obtained with Hg2 + . 相似文献
4.
Taras K. Antal Wayne Lo William H. Armstrong Esa Tyystjärvi 《Photochemistry and photobiology》2009,85(3):663-668
We measured the photosensitivity of an artificial tetranuclear oxo–Mn(IV) complex, [Mn4 O6 (bpea)4 ]Br4 , which has an adamantane-shaped {Mn4 O6 }4+ core. Illumination caused changes in the absorption spectrum of the compound consistent with a one-electron reduction in the compound. Bromide appears to be the most probable electron donor in the reaction system. Chemical modification of the cluster appears to destabilize it, predisposing it to reductive degradation. UV light was more efficient than visible light in causing the changes. The data support the suggestion that the natural oxygen-evolving Mn complex is photosensitive and can oxidize components of the oxygen-evolving complex in its excited state causing photoinhibition, and that photostability is an important issue in designing Mn complexes for artificial photosynthesis. Furthermore, light-induced oxidation of bromide by [Mn4 O6 (bpea)4 ]4+ may suggest that oxidation of chloride is involved in natural water splitting or has been involved during the evolution of the water-splitting enzyme. 相似文献
5.
Abstract— Stationary phase cultures of a DNA repair proficient Escherichia coli K-12 strain showed a release of intracellular material as assessed by three different methods (260 nm absorption; [methyl-3 H]thymidine leakage and 86 Rb+ leakage) after broad-band (Black-Light Blue) near-UV radiation but not after far-UV (254 nm) radiation. As a control response for membrane damage to cells, this leakage of intracellular material was also determined by each method after mild-heat (52°C) treatment of E. coli K-12. An action spectrum for the release of 86 Rb+ from E. coli K-12 after irradiation with monochromatic wavelengths, from 254 to 405 nm, is also presented. The action spectrum for lethality (F37 values) obtained for this strain, shows that leakage of 86 Rb+ occurs at fluences equivalent to or slightly less than fluences causing inactivation at wavelengths above 305 nm. In contrast, at wavelengths below 305 nm, leakage of 86 Rb+ from irradiated cells can be induced but only at fluences significantly greater than was required to cause cell inactivation. These results indicate, therefore, that near-UV radiation can induce a damaging effect on the cell's permeability barrier which may be significant in causing the death of the cell, whereas the effect is not significant in causing the death of cells by far-UV radiation where DNA damage is known to be the main cause of lethality. 相似文献
6.
HE Song LIU Qiuchen LI Yuanyuan WEI Fangfang CAI Songtao LU Yan ZENG Xianshun 《高等学校化学研究》2014,30(1):32-36
A novel water soluble chemosensor 1 based on rhodamine 6G spirolactam scaffold has been synthesized and characterized.Upon addition of a wide range of the environmentally and biologically relevant metal ions,chemosensor 1 shows a colorimetric selective Cu2+ recognition from colorless to pink confirmed by UV-Vis absorption spectral changes,while it also exhibits a fluorometric selective Hg2+ recognition by fluorescence spectrometry.An absorption enhancement factor over 17-fold with 1-Cu2+ complex and a fluorescent enhancement factor over 45-fold with 1-Hg2+ complex were observed.Their recognition mechanisms were assumed to be a 1:1 stoichiometry for 1-Cu2+ complex and a 1:2 stoichiometry for 1-Hg2+ complex,respectively,which were proposed to be different ligation leading to the ring-opening of rhodarnine 6G spirolactam.Furthermore,the detection limits for CU2+ or Hg2+ were 3.3 × 10-8 or 1.7x 10-7 mol/L,respectively. 相似文献
7.
Abstract— Perimycin, ouabain and elevation of extracellular K+ concentrations cause an increase in the fluence rate thresholds (white light) for the step-up photophobic response in Peranema trichophorum . Elevation of extracellular Na+ concentration decreases the thresholds for this response in comparison to the control level. The fluence rate threshold of perimycin-treated cells increases before the side effect of an antibiotic action appears. Removal of K+ ions from the medium of K+ -treated cells to a concentration of 1 mM depresses the threshold for the step-up response to the control level. By addition of K+ or Na + ions to perimycin- or ouabain-treated cells the threshold returns to the control value. It is suggested that the flagellar and cell membrane are responsible for changes of P. trichophorum photosensitivity. 相似文献
8.
I. B. C. Matheson 《Photochemistry and photobiology》1979,29(5):875-878
Abstract— The chemical reaction rate constant of bilirubin with singlet oxygen in basic aqueous solution has been redetermined to be 3.5 × 108 M-1 s-1 by a competitive technique using a 1,3-diphenylisobenzofuran in sodium dodecyl sulfate micelles. Bilirubin also physically quenches a singlet oxygen with a rate constant of 9 × 108 M -1 s-1 . The lifetime of singlet oxygen in D2 O solution has been determined to be 35 μ s . The absorption cross-section for the molecular oxygen 3 ∑g -→1 δ g + 1 v electronic transition at 1.06μn in aqueous solution is unexpectedly larger than the gas paase cross-section. 相似文献
9.
Abstract— The fluorescent properties of the rare-earth ion, Tb3+ have been utilized to probe the nature of cation-binding sites associated with thylakoid membranes. At low concentrations (< 100μ M ), Tb3+ was observed to inhibit the increase in chlorophyll a fluorescence normally seen on adding 5 m M MgCl2 (or 100 m M NaCl) to isolated, broken chloroplasts. We also observed under these conditions, the appearance of a new band around 280 nm in the excitation spectrum of Tb3+ ion fluorescence. However, similar changes in Tb3+ fluorescence could be observed in the presence of a membrane-free preparation of chloroplast coupling factor protein (CF1 ). From this and other results it is concluded that changes in Tb3+ fluorescence reflect an association of the ion with CF1 followed by intermolecular transfer of excitation energy from protein ligands (possibly un-ionized tyrosine residues) to the lanthanide. The interaction of Tb3+ with sites which control chlorophyll a fluorescence does not seem to modify Tb3+ fluorescence, suggesting that in this case, simple membrane-bound ligands such as carboxyl or phosphate groups are involved. 相似文献
10.
Abstract— Transient absorption spectra produced by laser flash photolysis of an aqueous solution of 8-methoxypsoralen (8-MOP) have been studied. The biphotonic production of hydrated electrons and of the radical ions, 8-MOP + and 8-MOP- is reported. The hydrated electron was found to react with ground state 8-MOP with k ˜ 3 × 1010 M -1 s-1 . In order to obtain a true triplet-triplet absorption spectrum. contributions from the radical ions were subtracted from the overall transient absorption. In addition, contributions from e- aq to the transient spectrum were removed by using N2 O, low laser intensity to minimize photoionization or by measuring the transient O.D. after the electron has decayed. These three methods each produced the same triplet-triplet spectrum which differs in the red region from previously reported spectra. 相似文献
11.
Paul A. Liddell John P. Sumida Alisdair N. Macpherson Lori Noss Gilbert R. Seely Kristine N. Clark Ana L. Moore Thomas A. Moore Devens Gust 《Photochemistry and photobiology》1994,60(6):537-541
Abstract Porphyrin-C60 dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels-Alder reaction. The porphyin singlet lifetimes of both the zinc (Pzn -C60 ) and free base (P-C60 ) dyads, determined by time-resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet-singlet energy transfer to C60 The lifetime of Pzn-1 C60 is -5 ps in toluene, whereas the singlet lifetime of an appropriate C60 model compound is 1.2 ns. This quenching is attributed to electron transfer to yield Pzn bull; +-C60 bull; -. In toluene, P-1 C60 is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of-10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C60 triplet. In the more polar benzonitrile, P-1 C60 underoes photoinduced electron transfer to give P• + -C60 bull; -. The electron transfer rate constant is −2 × 1011 s−1 . 相似文献
12.
Abstract— The fluoroquinolone antibiotics can induce skin photosensitivity in some patients and this has been ascribed to the generation of reactive oxygen species, such as singlet oxygen (O2 [1 Δg ]). We have studied the photochemical properties of the different ionized forms of the fluoroquinolone norfloxacin upon complexation with Mg2 + and Ca2 + ions, as it is proposed that the antibiotic exists mainly as a complex in the blood plasma. We found that the norfloxacin cation (pH < 6) shows no photodegradation after UVA irradiation and has a low quantum yield of O2 (1 Δg ) generation. The norfloxacin cation does not complex. Ca2 + or Mg2 + ions; when these ions are added to the solution, we observed no changes in the fluorescence quantum yields (φflu ) and singlet oxygen yields (φΔ ). In contrast, the neutral (6 ± pH > 8.5) and anionic (pH > 9) forms of norfloxacin are able to complex calcium and magnesium, and their generation of O2 (1 Δg ) is decreased by complexation. The neutral zwitterionic form and the anionic form also quench singlet oxygen by both chemical and physical pathways regardless of complex formation, while physical quenching is observed for the cation. At pH > 7.4, norfloxacin photobleaches and complexation to Ca2 + and Mg2 + increases the rate at which photobleaching occurs. Thus, both the pH of the medium and complexation with metal cations may affect the phototoxic potential of this antibiotic. 相似文献
13.
Abstract— p K values of ionisation equilibrium of thiazines dyes in their triplet state have been measured in aqueous solutions by spectroscopy. The triplet-triplet absorption bands, in the red part of the spectrum, are given for thionine, azurs and methylene blue. It is shown that, in the pH range 4–9, the equilibria investigated correspond to a second protonation of thiazines dyes that occurs in the triplet state:
3 TH+ + H+ →3 TH2 2+
designating by3 TH+ the thiazine cation similar to the species stable in neutral aqueous solutions. 相似文献
designating by
14.
Abstract— The spectra and molar absorbances of the HO2 and O2 - free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by 60 Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are 225 = 1400 ± 80 M -1 cm-1 and 225 = 2350 ± 120 M -1 cm-1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO2 and O2 - : K Ho2+HO2 = (8.60 ± 0.62) × 105 M -1 s-1 ; K Ho2+O2- = (1.02 ± 0.49) × 108 M -1 s-1 ; K Ho2+O2- < 0.35 M -1 s-1 . For the equilibrium HO2 → O2 - + H+ the dissociation constant is K Ho2 = (2.05 ± 0.39) × 10-5 M or p K HO2 = 4.69 ± 0.08. G (O2 - ) has been evaluated as a function of formate concentration. 相似文献
15.
Abstract— We have studied the influence of the heavy metal ions Ag+ and Hg2+ on the photoinactivation and photodimerization of transforming DNA and of bacteriophage. The rate of inactivation of Haemophilus influenzae transforming DNA by ultraviolet (UV) radiation was enhanced by a factor of 30 when it was complexed with Ag+ . This enhancement was correlated with a comparable increase in the rate of thymine dimerization. In contrast, mercuric ions led to a reduction in the rates of both inactivation and dimerization. When we examined the effects of these metal ions on the photobiology of bacteriophage, we again found that Ag+ enhanced and Hg2+ reduced the rate of ultraviolet inactivation. These results demonstrate that heavy metals may be useful tools for studying the photochemistry and photobiology of nucleic acids. 相似文献
16.
CALCIUM CONTROL OF PHOTOTACTIC ORIENTATION IN Chlamydomonas reinhardtii: SIGN AND STRENGTH OF RESPONSE 总被引:3,自引:0,他引:3
Abstract— Chlamydomonas reinhardtii responds to a blue light stimulus by an oriented swimming (phototaxis) toward or away from the stimulus source. In this study it is established that the sign and strength of the phototactic response are a complex function of extracellular [Ca2+ ], stimulus fluence rate, time of analysis after onset of stimulation and light pretreatment. At very low extracellular [Ca2+ ] the response is weak and usually negative. At [Ca2+ ] close to the preconditioning level, phototactic response becomes stronger and positive. As [Ca2+ ] is raised further, the initial (2 s) response remains positive but the long term (20 s) becomes negative and very strong. At extremely high [Ca2+ ] the cells become immobile. This bimodal behavior suggests that two different mechanisms determine the direction of the turn. Data cannot be explained in terms of a simple model. The model which accounts for most of the details of the behavior is that of Kamiya and Witman (1984), which proposes that positive response is triggered by a transient increase in intracellular [Ca2+ ] and negative response by a decrease below unstimulated level of Ca2+ , at least in the range of 10-9 -10-6 M [Ca2+ ]. The strong negative orientation which follows an initial positive response above this level of [Ca2+ ], in these experiments, is best explained by an adaptation of the cells due to an increased (on average) intracellular [Ca2+ ]. 相似文献
17.
Abstract 125 I- N 6 -(N-[6-N-{5-iodo-4-azidosalicyl}-aminohexyl]-aminocarbamoylmethyl)-nicotinamide adenine dinucleotide (125 I- N 6 -I-ASA-AH-NAD+ ) was synthesized by coupling N 6 -([6-aminohexyl]-carbamoylmethyl)-NAD+ with 4-azidosalicylic acid N-hydroxysuccinimide ester followed by radioiodination. The utility of 125 I-N 6 -I-ASA-AH-NAD+ as an effective site-directed photoprobe was demonstrated by the photolabeling of both glutamate dehydro-genase and 15-hydroxyprostaglandin dehydrogenase. Both enzymes can be saturated with labeled probe with apparent dissociation constants comparable to those reported for NAD+ . Photoincorporation of the probe into both enzymes was found to be protected specifically by NAD+ . These results indicate that 125 I- N 6 -I-ASA-AH-NAD+ can be a specific photoprobe for NAD+ -linked enzymes. 相似文献
18.
G. De Guidi S. Giuffrida G. Condorelli L. L. Costanzo P. Miano S. Sortino 《Photochemistry and photobiology》1996,63(4):455-462
Abstract— Photocleavage of DNA induced by naproxen and the correlated protective effect by some inorganic ions have been considered. The presence of a DNA complex is suggested and only associated naproxen seems to be responsible for the cleavage, for which the quantum yield of single strand breaks was calculated. The inorganic ions I- , Mn2+ , Co2+ and Cu2+ decrease naproxen-photoin-duced DNA cleavage. Iodide acts by a heavy atom mechanism, thus inhibiting naproxen photolysis and decreasing the amount of free radicals responsible for the photocleavage both in aerobic and anaerobic conditions. Metallic ions protect only within a range of concentrations, as for higher amounts damaging processes are observed. The protective efficiency of cations decreases with the increase of free drug concentration in the bulk of the solution, due to their involvement in the scavenging of naproxen radicals generated by photolysis of the free drug. In the presence of EDTA the cations show a better protective action. The most likely hypothesis is an inhibiting effect on the damaging processes via a redox cycle. The different behaviors of copper and of the two other cations can be justified by the influence of redox potentials of free and complexed metals and by the superoxide dis-mutase-like activity of copper. 相似文献
19.
Giuliano ColombettiFrancesco LenciPill-Soon Song† 《Photochemistry and photobiology》1982,36(5):609-611
Extracellular K+ ions above a critical concentration induce ciliary reversal in unstimulated Stentor coeruleus and suppress step-up photophobic response. This threshold concentration of K+ ions depends on the extracellular Ca2+ concentration, and the subsequent backward gyration and light-sensitivity suppression seem to depend on the relative concentrations of K+ and Ca2+ . The concentration of Ca2+ necessary to overcome K+ -mediated inhibition of phobic response and backward swimming increases non-linearly with increasing K+ concentration. The Ca2+ -blocking agent. D-600, selectively inhibits photophobic responses of Stentor , thus further confirming the role of Ca2+ ions in photosensory transduction of this ciliate. 相似文献
20.
G. T. MARKS E. D. LEE D. A. AIKENS H. H. RICHTOL 《Photochemistry and photobiology》1984,39(3):323-328
Abstract— Flash photolysis of neutral red between pH 1.3 and pH 11 yields the triplet species 3 DH2 +2 3 DH+ and 3 D. Both 3 DH2 +2 and 3 D exhibit first order decay with rate constants of 1.6 ± 0.3 × 104 s-1 but 3 DH+ decays within the lifetime of the flash. Over the entire pH range, ascorbic acid quenches the triplet, forming the semireduced radicals DH3 +2 DH2 + and DH, all of which exhibit second order decay with k = 1.8 ± 0.4 ± 108 M -1 s-1 most probably by recombination with semioxidized ascorbic acid. The dependence of the rate of decay of radical neutral red on the identity of reversible reductants supports the back-electron transfer mechanism, as does digital simulation of complex radical disproportionation schemes. In contrast to the efficient reduction of triplet neutral red by ascorbic acid, its reduction by EDTA is quite inefficient. 相似文献