摘要:

AbstractPulsed laser cross‐linking provides a means of introducing a covalent bond between proteins and the nucleic acids to which they are bound. This rapid cross‐linking effectively traps the equilibrium that exists at the moment of irradiation and thus allows examination of the protein‐nucleic acid interactions that existed. Laser irradiation may also induce photodestruction of protein and we have used the bacteriophage T4 gene 32 protein to investigate this phenomenon. Our results show that both nonspecific and specific photoproducts can occur, specifically at wavelengths where the peptide backbone of proteins is known to absorb. These results demonstrate that nonspecific photodegradation can be correlated with the formation of a specific photodegradation product. The formation of this product was monitored to show that product yield is nonlinearly dependent on laser power and wavelength. We have also investigated an unexpected photoproduct whose formation is dependent on the length of the polynucleotide to which the gene 32 protein binds and that further demonstrates the complexities of analyzing protein‐nucleic acid interactions through the use of UV laser cross‐linking. These data provide essential information for the establishment of appropriate conditions for future studies that use UV cross‐linking of protein‐nucleic a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04895.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe photooxidation ofN,N‐diethylhydroxylamine (DEHA) by Rose Bengal (RB) has been investigated in micellar and nonmicellar aqueous solutions. We measured the quantum yield of oxygen consumption forming H2O2and monitored two intermediates, the superoxide and diethylnitroxide radicals. When the pH was vaned, the quantum yield of oxidation remained constant for 6

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04896.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTriplet formation quantum yields (Φτ) of psoralen in a set of 17 pure solvents ranging fromn‐hexane to water and in dioxane: water mixtures were obtained by nanosecond laser flash photolysis. The triplet yield increases with solvent polarity. The extremum values are 0.009 and 0.545 inn‐hexane and water, respectively. Good correlations of the experimental Φτvalues with empirical “polarity” scales (Dimroth/Reichardt's ET[30], Kamlet/Taft's solva‐tochromic parameters β, and α, and Swains acity/basity AS/BS) were obtained: Ln(φT‐1‐ 1) = 8.86 ‐ 0.143ET(30) Ln(φT‐1‐ 1) = 4.40 ‐ 2.34τ‐ 1.70α Ln(φT‐1‐ 1) = 4.65 ‐ 3.72As‐ 1.12BsThe results are discussed in terms of the sensitivity of psoralen triplet quantum yield to solve

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04897.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract7‐Azatryptophan is proposed as an alternative to tryptophan as a photophysical probe in the study of protein structure and dynamics. Not only are the spectral characteristics of 7‐azatryptophan easily distinguishable from those of tryptophan, but this nonnatural amino acid is shown to be amenablc to incorporation into peptides. We present the first synthesis and purification of a synthetic peptide containing 7‐azatryptophan, NAc‐Pro‐7‐azatryptophan‐Asn‐NH2, which is shown to be a competitive inhibitor o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04898.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDimerization of chloroaluminum (III) phthalocyanine tetrasulfonates (AIPCS) has been observed in different aqueous alcoholic solvents at room temperature by absorption and fluorescence spectroscopic methods. Both absorption and fluorescence spectral bands of the dimer are red shifted byca550 cm‐1from the monomer Q bands in the corresponding spectra, suggesting that the interaction energy between the two monomer subunits is very weak. The fluorescence lifetime of the dimer is longer (ca9.5 ns) than that of the monomer (ca7–8 ns). These spectral behaviors of AIPCS dimer contrast with those of transition‐metallaloid phthalocyanine dimers, which usually have a nonfluorescent face‐to‐face stacking conformation. The dimer fluorescence is interpreted to be due to the fact that the lowest excited singlet state of the dimer is lower in energy than a charge‐resonance state, based on the excitoncoupling theory applied to the face‐to‐face slipping conformation. The dimerization constant determined spectrometrically decreases with an increase of water content in the aqueous alcoholic solution. Propanol and ethanol have been observed to be more effective than methanol in promoting dimerization. These results indicate that a specific interaction of water with AIPCS plays an important role in the inhibition of dimeri

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04899.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractKnowledge of the fluence distribution in biological tissue is essential for applications of lasers and light in medicine. A method using a photoactivable fluorophore as a chemical actinometer is presented to investigate the fluence (J/cm2) distribution in tissue‐simulating phantoms. Such a chemical actinometer provides high spatial resolution (≤20 μm) while minimizing the disturbance of the fluence distribution. The actinometer substance, nonfluorescent in its native state, is incorporated into an acrylamide gel. Upon absorption of 351 nm radiation (λact), the actinometer substance becomes a Ruorophorc, which is excited at λex≤ 485 nm. Thus the spatial distribution of the emitted fluorescence (λem≤ 515 nm) in the actinometer represents the fluence distribution of the activating radiation. Using histological techniques, 20 μm sections are cut from gel‐like optical phantoms containing the actinometric substance. The fluorescence intensity in the section is recorded under a standard fluorescence microscope equipped with a sensitive video camera. To simulate different biological tissues, the scattering and absorption properties of the gel phantoms arc varicd over a wide range. The experimentally obtained fluence distributions are compared with theoretical models of light distribution i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04900.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractExperiments with human hepatoma PLC/PRF/5 cells and human embryo skin fibroblasts involving the use of three different tests (colony formation, Trypan blue exclusion, labeled thymidine incorporation) have demonstrated a significantly higher photosensitizing activity of chlorin e6conjugates with internalizable ligands as compared to that of chlorin e6itself. Receptor‐mediated internalization of chlorin e6conjugates ensures a greater photosensitization of cells than binding of those conjugates to cell surface receptors. The suitability of such conjugates that permit the delivery of a photosensitizer to sensitive intracellular targets is discusse

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04901.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe (1H‐indenyl)thiophene derivatives 2 and 3 were recently reported to be excellent singlet oxygen sensitizers. comparable to α‐terthienyl (1). The phototoxicity of these compounds was compared, using human erythrocytes,Aedes aegyptimosquito larvae.Daphnia magna. and fish (fathead minnows,Pimephales promelas). The known ranking of the photooxidation properties was found to be a good predictor of phototoxic properties in erythrocytes and mosquito larvae but not in daphnias. All three compounds photosensitized the cleavage of supercoiled pBR322 DNA to the same ex

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04902.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have compared the photodynamic activities of hematoporphyrin (HP) and protoporphyrin (PP) on isolated rat liver mitochondria by measuring the decline of the respiratory control ratio (RCR) after irradiation at 365 nm. Before addition to the respiratory mcdium, the dyes were dissolved in phosphate‐buffered saline (PBS) or incorporated into unilamellar liposomes of dipalmitoyl‐phosphatidylcholine (DPPC), sometimes enriched with cholesterol (Chol) or cardiolipin (Card), which are naturally present in mitochondrial membranes. Chol and especially Card strongly increase the porphyrin uptake by mitochondria. In all experimental conditions, PP is taken up by mitochondria to a higher extent than HP. Nevertheless, under conditions giving the same amount of mitochondriabound dye, HP is a morc efficient photosensitizer than PP. As the efficiency of singlet oxygen production has been shown to be equivalent for the two porphyrins in monomeric state, the resulting photobiological effects are explained in terms of different localization of HP and PP in the mitochondrial membrancs. In particular, HP preferentially localizes in the protein‐rich polar domains of the inner mitochondrial membrane, whereas PP dissolvcs in the lipid regions of the mcmb

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04903.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAmino or polyamino derivatives of naphthalene (N‐H), anthracene (A‐H) and 8‐alkoxypsoralen (PSR‐H) were prepared along with their monobrominatcd analogs (N‐Br, A‐Br and PSR‐Br). The ammonium salts of these compounds are all water soluble and bind strongly to calf thymus DNA and to λ phage, a double‐helical DNA, protein‐coated virus. Binding of the sensitizer to DNA occurs, presumably by a mixture of hydrophobic, intercalative and electrostatic interactions. Relative binding constants to calf thymus DNA and to λ phage were measured by the cthidium bromide fluorescence quenching assay. In general the brominated analogs bind more tightly to calf thymus DNA and to the virus than to the nonhalogenated analogs. It is demonstrated that the brominated aromatics are much more effective at inactivating λ phage upon photoactivation (λ 310 or 350 nm) than are their nonbrominated analogs. At identical sensitizer concentrations (by weight) and light flux N‐Br, A‐Br, and PSR‐Br produce 5–6 more logs of viral inactivation than their nonbrominated counterparts (N‐H, A‐H and PSR‐H, respectively). The bromine effect may originate from light‐induced electron transfer and subsequent cleavage of the C‐Br bond of the sensitizer radical anion bonds to form aryl radicals. Singlet oxygen cannot be responsible for the viral inactivation because the brominated sensitizers are equally effective in the presence and absence of oxygen. Dithiothreitol does not protect λ phage from light‐induced inactivation by the brominated sensitizer thereby demonstrating that the photogenerated reactive intermediates responsible for the effect are complcxed to the vi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb04904.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY