摘要:

Abstract:A model for magnetic field effects in biological systems is proposed. This model employs the basic concepts of the radical pair mechanism, and predicts that magnetic fields will increase the average radical concentration, lengthen their lifetime and enhance the probability of radical reactions with cellular components. The relevance of these effects in relation to cancer initiation, promotion and progression is discussed.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09660.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:Very little has been done in the direct study of nonradiative decays of Trp, indole and derivatives, in spite of their relatively low fluorescence quantum yields. Time‐resolved photoacoustic calorimetry is an ideal technique for this kind of study: it is very sensitive in the detection of small amounts of heat released and, in principle, allows a broad band of temporal resolution. The photoacoustic apparatus used for our measurements offers a temporal window between 10 ns and 10 μs. The analysis of the waveforms, based on a particular deconvolution method, simultaneously gives the fraction of energy released and the associated lifetime. In a broad sense, time‐resolved photoacoustic spectroscopy can be seen as a complementary method to traditional radiative techniques such as static, time‐resolved fluorescence and flash photolysis. The present work presents studies of Trp in different solvents in order to acquire new information about the interaction of this chromophore with solvents. From our measurements the high sensitivity of Trp to solvents is confirmed. The formation of complexes is evident at the excited state (exciplexes), between the chromophore and one or more molecules of solvent. These exciplexes are characterized by having an energy different from that of the singlet and triplet of Trp. Moreover, photoacoustic measurements detect, in water, the presence of another electronic state, which seems to have characteristics similar to a triplet‐like state reported in ot

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09661.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:The interaction of 8‐methoxypsoralen (8‐MOP) with synthetic eumelanin was investigated using static and time‐resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8‐MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen‐melanin complexes, the photoacoustic parameters of 8‐MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground‐state level, whereas the singlet excited state of 8‐MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photose

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09662.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:The solid‐matrix luminescence properties and several calculated photophysical parameters of two important products from the benzo(a)pyrene‐DNA adducts were compared. The products were benzo(a)pyrene‐r‐7,t‐8,9,c‐10‐tetrahydrotetrol (I‐1) and 7R,8S,9S‐trihydroxy‐10‐(N2‐deoxyguanosyl‐3′‐phosphate)‐7,8,9,10‐tetrahydroben‐zo(a)pyrene (BPDE‐dG). The solid‐matrix luminescence data were obtained for I‐1 and BPDE‐dG adsorbed on two different solid matrices, namely, 1%α‐cyclodextrin (CD)/NaCl and 25% trehalose/NaCl and at two different temperatures (93 K and 296 K). The 25% trehalose/NaCl gave higher fluorescence and phosphorescence quantum yields from both I‐1 and BPDE‐dG in contrast to the 1%α‐CD/NaCl matrix. The BPDE‐dG showed lower fluorescence quantum yields on the solid matrices compared to I‐1. The lower fluorescence quantum yields for BPDE‐dG were attributed to a photoinduced electron transfer mechanism. In contrast to the room‐temperature solution fluorescence of BPDE‐dG, BPDE‐dG gave rather high fluorescence quantum yields at room temperature when adsorbed on the two solid matrices. From solid‐matrix luminescence quantum yields and solid‐matrix luminescence lifetimes, many photophysical parameters were calculated and compared. Several differences among the rate constants were noted with the two solid matrices for BPDE‐dG and I‐1. For example, BPDE‐dG showed internal conversion at 296 K with 25% trehalose/NaCl, but no internal conversion was observed at 93 K with this solid matrix. Also, for BPDE‐dG the phosphorescence rate constants at 296 K and 93 K were very small with 25% trehalose/NaCl, but the intersystem crossing rate constants from the triplet state to the ground state were very large. The results from this work show how solid‐matrix luminescence can be empl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09663.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:The individual tryptophanyl contributions to the near‐ultraviolet dichroic activity of apomyoglobin in its native conformation have been resolved. This was accomplished by comparing the spectra of two classes of apomyoglobin with different aromatic residue contents and observing the effect of a specific modification of indole residues. The circular dichroism (CD) spectra of apomyoglobins containing two tryptophanyl residues,i.e.Trp A‐5 and A‐12, show the presence of a positive peak centered at 292 nm, attributable to indolic chromophore, which is missing in the CD spectrum of tuna apomyoglobin possessing only Trp A‐12. Moreover, the specific modification of Trp A‐5 by 2‐hydroxy‐5‐nitrobenzyl bromide is shown by the lack of the 292 nm peak and the appearance of a positive band at longer wavelength. The pH dependence of the position of this band suggests that it arises from the 2‐hydroxy‐5‐nitrobenzyl moiety. The results suggest that Trp A‐12 does not substantially contribute to the optical activity

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09664.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:A photochemical kinetic method of measuring small values of efficiency of fluorescence resonance energy transfer (FRET) between special probes is proposed. The FRET efficiency (ω) is determined from kinetics of the photochemical reaction of the energy acceptor sensitized by FRET from the energy donor. The choice of an appropriate donor‐acceptor pair permits the minimization of background reactions. Application of the method is demonstrated by the detection of FRET from 2,5‐bis(5‐tert‐butyl‐2‐benzoxasolyl)thiophen (BBOT) to acridine orange (AO) in phospholipid vesicles. Photobleaching of AO in the presence of CBr4was applied as a photochemical reaction of the acceptor. The reaction was monitored by steady‐state fluorescence measurements. The FRET measurements were carried out by the proposed technique when the probe/lipid ratio and ω were as small as 1.1 × 10−5M/Mand 0.0017, respectively. Under these conditions, the rate constant of AO photobleaching was increased by 26% as compared with that of the reference sample without BBOT. The results suggest that applications of the technique may be useful in the study of the m

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09665.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:A method is described utilizing the tetrazolium salts neotetrazolium chloride (NTC), triphenyltetrazolium chloride (TTC), C,N‐diphenyl‐N′‐4,5‐dimethylthiazol‐2‐yrtetrazolium bromide (MTT) and various substrates to elucidate damage to the mitochondrial electron transport chain of intact cells followingin vitrophotodynamic therapy (PDT). Using this methodology, a portion of the dark toxicity manifested by Photofrin II (PII) was found to occur prior to entry of electrons into the transport chain through Complex I, as evidenced by the fact that the inhibition of MTT reduction was reversible by the addition of malic acid to the culture media. A second site of dark toxicity was found to be Complex IV (cytochrome oxidase). After photoirradiation of the cells, Complex I was found to be affected since malic acid could no longer reverse the inhibition of MTT reduction but it could be reversed by the addition of succinic acid, whose electrons enter the transport chain at Complex II. A second and more sensitive site of photoirradiation damage was found to be Complex IV. A region near cytochrome C was also affected by photoirradiation but appreciably less so than noted for Complexes I and IV. A kinetic analysis of MTT and TTC reduction following photoirradiation indicated that MTT reduction was sustained at a normal rate for 1 h after which it slowed down and eventually plateaued. In contrast, TTC reduction was found to be inhibited almost immediately indicating Complex IV is extremely susceptible to photoirradiation damage. Compared to other assays of mitochondrial function requiring subcellular fractionation, the use of tetrazolium salts is simpler to perform and can be done using physiologically releva

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09666.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:We compared the photodynamic effects of thiopyronine (TP) and visible light, and 8‐methoxypsoralen (8‐MOP) and ultraviolet A (UV‐A) light, on growth, colony forming ability and RNA synthesis in a repair‐proficientSaccharomycesstrain and three mutants deficient in DNA repair mechanisms (DNA repair assays). With 8‐MOP and UV‐A repair‐deficient mutants were significantly more sensitive than the repair‐proficient strain indicating that the system is sensitive for the detection of DNA damage. With TP and visible light, the photodynamic effects were comparable in the mutants and the control, indicating no DNA damage. These results support previous work showing that the main target of TP photosensitization in eukaryotes is

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09667.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:A variety of naturally occurring photosensitizers of plant origin were tested for their ability to cause ultraviolet‐A (UVA)‐dependent inhibition of photosynthetic14CO2fixation in leaf disks ofPisum sativumL. At 0.1 mMconcentrations and 60 min UVA irradiation, α‐terthienyl was strongly inhibitory, harmine and sanguinarine inhibited to a lesser degree, and curcumin, 8‐methoxypsoralen and nordihydroguaiaretic acid had no effect under the conditions tested. Alpha‐terthienyl + UVA treatments that fully inhibited14CO2fixation had no effect on fresh weight, chlorophyll or protein content of the tissue. Chloroplast malate dehydrogenase and glyceraldehyde‐3‐phosphate dehydrogenase were inhibited 45% and 29%, respectively, by α‐terthienyl + UVA treatment. Electron transport from H2O to the reducing side of photosystem I was inhibited to a similar extent, suggesting interference with the reductive activation of chloroplast enzymes. Alpha‐terthienyl + UVA‐treated tissue exhibited a seven‐fold increase in leakage of labeled photosynthate into the external medium. Treated leaf disks showed no ability to recover14CO2fixing ability over a 24 h period. These results indicate photosensitized damage at the level of the thylakoid membranes resulting in partial loss of electron transport capability and more general damage to chlorop

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09668.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract:Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium‐selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non‐singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygenversusnon‐singlet oxygen modification of biological sy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb09669.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY