摘要:

AbstractSteady‐state and dynamic fluorescence properties of 6‐lauroyl‐2‐dimethylaminonaphthalene (Laurdan) have been used to ascertain the coexistence of separate phase domains and their dynamic properties in phospholipid vesicles composed of different mole ratios of dilauroyl‐ and dipalmitoyl‐phosphatidylcholine (DLPC and DPPC, respectively). The recently introduced generalized polarization together with time‐resolved emission spectra have been utilized for detecting changes. The results indicate the coexistence of phospholipid phase domains in vesicle compositions in the range between 30 mol% and 70 mol% DPPC in DLPC. Below and above these concentrations a homogeneous phase is observed, with averaged properties. In the case of coexisting phase domains, the properties of each individual phase are largely influenced by the presence of the other phase. Implications on fluctuations between the coexisting phases and on the size and shape of domains

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02309.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe exchange of subunits between oligomer protein particles depends upon a cycle of dissociations and associations. To examine the dynamics of these cycles we have employed two methods based on the transfer of excitation energy between fluorochromes attached to different subunits of protein oligomers, at various temperatures and pressures. In the heterotransfer method, identical solutions independently labeled with two different fluorophores, donor D and acceptor A, are mixed. The fluorescence spectrum permits the determination of the subunit exchange by the increase in A and decrease in D fluorescence as mixed AD oligomers are formed. In the homotransfer method the aggregates are labeled with fluorescein to the extent that, ideally, each subunit carries a fluorophore. The emission is strongly depolarized because sufficiently often it takes place after a transfer to a fluorophore oriented differently from the one originally excited. Both dissociation and subunit exchange with unlabeled material result in an increase in polarization and can be independently determined by the homotransfer method. Both homo‐ and heterotransfer have been employed in the study of the effect of temperature on the stability of the aggregates and the relation between the rate of dissociation and the rate of exchange when dissociation of oligomers is induced by hydrostatic pressur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02310.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFamilial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant syndrome in which clinically euthyroid patients have elevated total thyroxine levels. These high serum thyroxine levels are traceable to altered binding of thyroxine to the patient's albumin. Albumin from FDH patients and normal volunteers have been purified. Reverse‐phase and ion‐exchange high performance liquid chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis on the FDH‐human serum albumin (HSA) samples show a single band that comigrates with normal HSA. In both protein solutions the intrinsic fluorescence, upon 280 nm excitation, is predominantly due to the single tryptophan residue. The quantum yield of this intrinsic fluorescence in the FDH‐HSA solutions is, however, reduced relative to that of HSA. Furthermore, the “average” lifetime value of the tryptophan emission in the FDH‐HSA sample is less than that of normal HSA, consistent with its reduced quantum yield. The binding of thyroxine to both albumins effectively quenches the tryptophan emission probablyviaa nonradiative energy transfer mechanism. Time‐resolved data suggest that the albumin from the dysalbuminemic patients is actually an approximately equimolar mixture of normal HSA and FDH‐HSA indicative of heterologous expression. Quenching of the intrinsic HSA and FDH‐HSA fluorescence by serial additions of thyroxine showed enhanced quenching of FDH‐HSA relative to HSA at any T4 to albumin mole ratio, therefore supporting earlier reports of increased thyrox

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02311.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSteady‐state fluorescence properties of 6‐dodecanoyl‐2‐dimethylaminonapththalene (Laurdan) have been used to determine the coexistence of separate lipid‐phase domains in apical brush border membrane vesicles isolated from the rat renal cortex. The temperature dependence of generated polarization has been utilized to quantitate the lipid phases. Finally, the effect of cholesterol enrichment on these parameters has been studied. The results indicate the coexistence of lipid‐phase domains in brush border membranes based on the values of the generalized polarization and assuming that the membrane state can be described by coexistence of gel and liquid crystalline state. At 37°C, approximately19–32% of the brush border membrane lipids are in the gel phase, and cholesterol enrichment causes a further concentration‐dependent increase in the gel phase of brush border

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02312.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractHuman erythrocytes were separated into five fractions representing different age groups. In each group phospholipid inside‐outside translocation was determined by quantitation of the amino phospholipids phosphatidylserine and phosphatidylethanolamine and their lyso‐derivatives by thin layer chromatography. To assess the role of transbilayer phospholipid distribution in the recognition and fusion of vesicular stomatitis virus (VSV) and human aged erythrocytes, we monitored the fusion kinetics using the octadecylrhodamine dequenching assay.Fusion of VSV with each single group of red blood cells (RBC) was not detectable with the youngest cells (Fl group) but increased with RBC aging (F2‐F5 groups). The same increase in fusion was observed with microvesicles generated from RBC in which aging was mimicked by incubating the cells with Ca2+in the presence of the Ca2+ionophore A23187.Conversion of the aminophospholipids to the trinitrophenyl derivative by reaction with trinitrobenzensulfonate completely inhibits fusion on ghosts in which aging was artificially induced by translocation of aminophospholipids in the outer leaflet (symmetric ghosts).These results indicate that RBC become susceptible to VSV fusion during aging and in all pathology related to the aging pr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02313.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe peptide hormone adrenocorticotropin and a related peptide were studied in solution and in interaction with a model system of membranes (small unilamellar vesicles of dipalmitoylphosphatidylcholine and 17% dimyristoylphosphatidylglycerol)viafluorescence spectroscopy. In aqueous solution, intramolecular distances between the fluorescent residues R(Tyr2‐Trp9) = 9.2 Å and R(Trp9‐Tyr23) 18 Å were obtained, in agreement with molecular models.Interaction of the peptide with the negatively charged membrane is evident from the alteration of the Trp photophysical parameters (quantum yield, fluorescence spectra and anisotropy), with a partition constant between the lipidic and aqueous phase ofKp =1–2 times 103.The existence of two populations of Trp in the membrane, which are distinctly accessed by acrylamide, was concluded from the tryptophan fluorescence quenching study; the two fractions are located near the membrane interface as inferred from its fluorescence quenching by the 5‐doxylstearate and 16‐doxylstearate lipophilic quenchers. This result is further supported by energy transfer experiments to the 3‐(9‐anthroyloxyl)stearic acid and 12‐(9‐anthroyloxyl)

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02314.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe changes in plasma membrane polarity of polymorphonuclear leukocytes (PMN) during the activation of the respiratory burst were investigated by measuring the steady‐state fluorescence emission spectra of 2‐dimethylamino(6‐lauroyl) naphthalene (Laurdan), which is known to be incorporated at the hydrophobic‐hydro‐philic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady‐state emission blue shift in nonpolar solvents, with respect to polar solvents. Our results show a blue shift of the fluorescence emission spectra of Laurdan during activation of PMN with phorbol myristate acetate or AT‐formyl‐methionyl‐leucyl‐phenylalanine. These results suggest that the activation of the respiratory burst of PMN is accompanied by a decrease in polarity in the hydrophobic‐hydrophilic interface o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02315.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPhotosensitized splitting ofcis‐syn‐andtrans‐syn‐l,3‐dimethyluracil dimers by 2′,3′,4′,5′‐tetraacetylri‐boflavin in acetonitrile containing a trace of perchloric acid was studied by laser flash photolysis. Protonation of the flavin prior to excitation resulted in excited singlet and triplet states that abstracted an electron from the dimers and yielded the protonated flavin radical (F1H2′+), which was detected by absorption spectroscopy. Electron abstraction by the excited singlet state predominated over abstraction by the triplet state. Approximately one‐third to one‐half of the excited states quenched by thetrans‐syndimer yielded F1H2+, the balance presumably undergoing back electron transfer within the geminate radical ion pair generated by the initial electron transfer. A covalently linked dimer‐flavin exhibited very inefficient flavin radical ion formation, consistent with the known low efficiency of dimer splitting in this system. These results constitute the first identification of a flavin radical ion intermediate in photosensit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02316.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dye‐sensitized photooxidation ofl‐histidine (His) andl‐methionine (Met) and their simplest dipeptides with glycine (Gly) (His‐Gly, Gly‐His, Gly‐Met) and Met‐methyl ester (Met‐ME) mediated by singlet molecular oxygen (O2[g]) was studied.The overall rate constants in acetonitrile‐H2O (Kt) for O2(1g) quenching were measured by time‐resolved phosphorescence detection. In H2O a competitive kinetic method was employed. In both solvents the reactive rate constants (Kt,) were determined to discriminate between the overall and physical contributions to the quenching. The kinetic and mechanistic aspects of the interaction are discussed.For His‐Gly, the peptide bond has practically no effect on the kinetics of photooxidation. For Gly‐His the overall rate constant is much higher than that for His and His‐Gly, in both H2O and acetonitrile‐H2O. The main contribution tok1(for Gly‐His) is the physical quenching of O2(1g)‐ In water thekt/krratio for free His and His‐Gly is 1.0, reaching a value of 2.0 in the organic solvent‐H2O mixture. The rates of‐NH2loss upon sensitized photooxidation in all cases parallel the trend ofkrvalues. The main results for the His series indicate that: (1) a polar environment favors autoprotection (i.e.an increase in the contribution of physical quenching) against photodynamic effects; (2) only the rate constant for reactive interaction with O2[g] does not depend on the location of the peptide bond involving His.For Met derivatives thekt, values are higher in both solvents than that for free Met. Only for the free amino acid in H2O is the interaction with O2(1g) totally reactive. For Gly‐Met and Met‐ME the physical quenching prevails:kt, is, in both solvents, about one order of magnitude higher thankr. According to our results on ‐NH2loss and on the basis of previous investigations by others, the photooxidative products distribution in the Met series indicates that Gly‐Met yields only dehydroMet, whereas Met and Met‐ME produce a mixtur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02317.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have investigated the effect of added Si02on the photochemistry of anthracene, 1, in cyclohexane. Adsorption of 1 onto the Si02surface from cyclohexane follows a Freundlich adsorption isotherm indicating interactions between 1 and the surface over a distribution of adsorption sites. In the absence of oxygen, addition of Si02to a cyclohexane solution of 1 leads to a significant increase in the rate of photolysis without a large concomitant change in product identity. The 9,10‐photodimer of 1 is the major product under oxygen‐deficient conditions. In the presence of oxygen, added Si02has dramatic effects on both the photoproduct distribution and the kinetics of photodecomposition. The complicated mixture of oxygenated products formed from photolysis in oxygen‐containing slurries is proposed to arise from thermal decomposition of a single primary photoproduct, anthracene‐9,10‐endo‐peroxide. The polarity/polarizability of the Si02/cyclohexane interface is considered to be a major factor influencing the rate of photolysis in the oxygenated Si02/cyclohexa

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb02318.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY