ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06922.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06923.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Methods for the controlled synthesis of modified protein photosensitizers which maximize affinity‐controlled energy transfer are discussed. Modified proteins containing covalently linked benzophenone groups were prepared by the reaction of bovine serum albumin withp‐benzoylbenzyl bromide under conditions limiting the number and locations of the introduced benzophenone chromophores. The mechanism of energy transfer responsible for quenching of triplet photochemical reactions of the modified proteins was explored using water soluble quenchers. In addition, methods were employed to determine the magnitude of the contribution of the affinity‐controlled mechanism for energy transfer in these systems. The utility of sodium‐cis‐8‐methylene‐4,9‐decadienoate as a triplet energy transfer indicator for macromolecular systems was demonstrated using the modified proteins as sensitizers. The trienoic acid was prepared starting with the known 4‐methylene‐5‐hexenal by the Wittig reaction with 3‐ethoxycarbonylpropylidene triphenylphosphorane followed by saponification. Triplet sensitized irradiation of this trienoic acid usingp‐benzoylbenzyltriethylammonium chloride as sensitizer led to production of endo‐ and exo‐1‐vinyl‐5‐(3‐carboxyethyl)bicyclo[2.1.1]hexane along with thetransacid. Characterization of the bicyclohexane products was made on the basis of spectroscopic evidence. Results demonstrate that quenching of the intramolecular photoreactions of the modified proteins by trienoic acid must be a result of triplet energy transfer, since irradiation of these modified proteins in the presence of the trienoic acid salt led to the char

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06924.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Ultraviolet irradiation of photosensitive molecules like phenothiazine derivatives leads to the formation of short lived free radicals which are able to reduce stable nitroxide free radicals generally used as spin labels. The measurement of the electron spin resonance signal decay of nitroxides offers a tool for studying the photochemical reaction of phenothiazine derivatives in solution at room temperature, in a 10‐5to 10‐2Mconcentration range. Analysis of the reaction mechanism shows that the paramagnetic nitroxide is an efficient quencher of the phenothiazine triplet state; this reaction was used to demonstrate the influence of the solvent, quenching by oxygen and the role of the chemical structure of six phenothiazine derivatives on their photoreactivity in sol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06925.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The spectral characteristics of the emission observed from tropolone, α‐methoxy‐tropone and colchicine in EPA at 77 K are reported. Luminescence polarization, lifetime, quantum yield and energy transfer experiments provide evidence that the luminescence observed is S1→ S0fluorescence and that the lowest excited singlet state is π, π* The two compounds α‐methoxy‐tropone and colchicine have been found to exhibit dual luminescence. No phosphorescence could be detected in these three molecules. The photophysical processes for each molecule are discussed and their respective energy level diagrams are

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06926.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Absorption and fluorescence polarization spectra, as well as absolute fluorescence quantum yields, and lifetimes of phycobiliproteins separated from intact phycobilisomes ofPorphyridium cruentum, Nostoc sp.andFremyella diplosiphonwere measured. Two different types of phycoerythrin, in addition to phycocyanin and allophycocyanin, were separated from bothPorphyridium cruentumandNostoc sp.phycobilisomes. They were distinguishable by the shape of their absorption spectra, values of fluorescence quantum yields and their limiting polarization. Phycobilisomes ofFremyella diplosiphonhad a type of phycoerythrin that was different from the above kinds. By the use of fluorescence quantum yields and lifetime data, the values of natural lifetimes, the decadic molar extinction coefficients, as well as Förster's critical distancesR0for excitation energy transfer, between phycobiliproteins in phycobilisomes, were estimated. The values obtained of Förster's critical distances indicate that for most efficient energy transfer from phycoerythrin to allophycocyanin, the outer layers ofPorphyridium cruentumandNostoc sp.phycobilisomes should be composed of bangiophycean, phycoerythrin and cyanophytan phycoerythrin‐II respect

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06927.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Quantum yield and fluorescence polarization determinations on phycobilisomes and their constituent phycobiliproteins show that phycobilisomes are energetically effective macromolecular structures. Energy migration within the phycobilisome to allophycocyanin, the longest wavelength absorbing and emitting phycobiliprotein, was indicated by the predominant allophycocyanin fluorescence emission which was independent of the phycobiliprotein being excited. The high efficiency of the energy migration inside the phycobilisome was reflected by the low polarized fluorescence. Excitation of phycobilisomes in the region of major absorption (500–650 nm) resulted in degrees of fluorescence polarization between +0.02 and –0.02, whereas in isolated phycobiliproteins the values were 2 to 12 times greater. Furthermore, 94–98° of the excitation energy of phycoerythrin was transferred to phycocyanin and allophycocyanin as determined from comparisons of fluorescence spectra of intact and dissociated phycobilisomes. The fluorescence quantum yields of phycobilisomes were about 0.60–0.68, very similar to that of pure allophycocyanin in solution (0.68). Phycobilisomes isolated fromFremyella diplosiphonandNostocsp. (blue‐gree algae) have respective quantum yields of 0.68 and 0. 65, and those isolated fromPorphyridium cruentum(red alga), about 0.60. InFremyella diplosiphonandNostocsp., which showed a striking adaptation to different wavelengths, the phycobilisome quantum yields only varied from 0.68 to 0.67 and from 0.65 to 0. 60, respectively. The mean transfer time, calculated on the basis of experimental results, was about 280 ± 40 ps for transfer of excitation from the phycoerythrin to the phycocyanin layer in phycobilisomes. This time corresponds to the mean number of jumps, about 28, of the excitation in the phycoerythrin layer before it is captured by phycocyanin. These values are in reasonable agreement with the values of 250 ± 30 ps and 25 jumps, calculated on the basis of a phycobilisome model (ofPorphyridium cruentum) and Pearlstein's theory of energy migration devised for a three‐dimensional photosynthetic unit. It was also shown that Paillotin's theory of energy migration predicts similar values for mean transfer time and mean number of jumps, if one assumes that phycocyanin is a perfect sink for phycoery

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06928.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Anin vitroassay is described for the quantitative conversion of nonphototransformable protochlorophyllide into phototransformable protochlorophyllide. The assay involves: (a) the conversion of exogenous nonphototransformable protochlorophyllide into phototransformable protochlorophyllide in the dark, and (b) the quantitative monitoring of this conversion by the disappearance of the phototransformable protochlorophyllide as it is converted to chlorophyllideaby a single, 15sillumination. This was achieved under conditions where no significant photodestruction of protochlorophyllide occurred. The formation of phototransformable protochlorophyllide from nonphototransformable protochlorophyllidein vitrowas further demonstrated by the conversion of exogenous nonphototransformable [14C]protochlorophyllide into [14C]chlorophyll. This was achieved in three steps: (a) the conversion of nonphototransformable [14C]protochlorophyllide into phototransformable [14C]protochlorophyllide in the dark; (b) the conversion of phototransformable [14C]protochlorophyllide into [14C]chlorophyllideaby a single 15sillumination; and (c) the esterification of the newly formed [14C]chlorophyllideato yield [14C]chlorophyll. The extent of these reactions was monitored by the incorporation of the14C‐label into chlorophyll. About 96% of the radioactivity in the [14C]chlorophyll fraction was found in [14C]chlorophy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06929.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—In order to determine the timing of the change in the state of DNA in bacterial spores during the course of germination, L‐alanine‐induced germination ofBacillus cereusspores was interrupted by 0.3MCaCl2as an inhibitor, and the resulting semi‐refractile spores (spores at the end of the first phase of germination) were examined on the UV‐resistance and the photoproduct formation.Upon UV‐irradiation, these spores, still having a semi‐refractile core as observed under a phase‐contrast microscope, gave rise to mainly the cyclobutane‐type thymine dimer. It was concluded that change in the state of the spore DNA occurs early in the process of germination, i.e. before the refractility of the core was lost.It was also found that CaCl2markedly prolonged the duration of the transient U

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06930.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

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 (<100μM), Tb3+was observed to inhibit the increase in chlorophyllafluorescence normally seen on adding 5 mMMgCl2(or 100 mMNaCl) 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 CF1followed 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 chlorophyllafluorescence does not seem to modify Tb3+fluorescence, suggesting that in this case, simple membrane‐bound ligands such as carboxyl or phosphate groups

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06931.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY