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At least 19 recordsLinked to original sources

PubMed1978

Enhancement of banding patterns in human metaphase chromosomes by energy transfer.

Intermolecular energy transfer between appropriately chosen pairs of dyes can be used to induce or enhance banding patterns in human metaphase chromosomes. Energy transfer, calibrated by fluorometric studies on soluble dye.DNA complexes, can also be detected by photometric measurements on cytological preparations of metaphase chromosomes stained with pairs of fluorochromes. If a fluorescent dye with one type of binding or quantum yield specificity (e.g., quinacrine, 33258 Hoechst, or chromomycin A(3)) is employed together with a counterstain (e.g., actinomycin D, 7-aminoactinomycin D, or methyl green) exhibiting a complementary base pair binding specificity and satisfying spectral overlap criteria for energy transfer, contrast in fluorescence from the first dye is enhanced in specific subsets of standard chromosome bands. Extensive energy transfer presumably suppress donor fluorescence except in chromosomal region containing clusters of at least 20 base pairs predominantly of one type, within which the donor but not the acceptor can bind and fluoresce. Quinacrine-bright polymorphic regions are especially resistant to fluorescence quenching by counterstains with G.C binding specificity, strengthening the evidence that these latter regions are highly enriched for A.T base pair clusters. The ability to highlight selectively many such polymorphic regions may prove of further, practical, utility in a number of cytogenetic problems.

Chromosomes, Human↗

PubMed1978

Energy transfer and site of energy trapping in photosystem I.

Studies of mutants of Chlamydomonas reinhardi deficient in the chlorophyll . protein complex CP1 show that energy transfer occurs between at least three Photosystem I units. Evidence for the connection of the Photosystem I units is also obtained by studying their optical cross-section in wild-type cells in which a fraction of the Photosystem I centers are inactivated. The site of energy trapping in the Photosystem I unit is shown to be the photochemical center itself and not the surrounding long-wavelength absorbing forms of chlorophyll.

Chlamydomonas↗

PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part II. In the isolated light harvesting complex (phycobilisomes).

The transfer of excitation energy between phycobiliproteins in isolated phycobilisomes has been observed on a picosecond time scale. The photon density of the excitation pulse has been carefully varied so as to control the level of exciton interactions induced in the pigment bed. The 530 nm light pulse is absorbed predominantly by B-phycoerythrin, and the fluorescence of this component rises within the pulse duration and shows a mean 1/e decay time of 70 ps. The main emission band, centred at 672 nm, is due to allophycocyanin and is prominent because of the absence of energy transfer to chlorophyll. Energy transfer to this pigment from B-phycoerythrin via R-phycocyanin produces a risetime of 120 ps to the fluorescence maximum. The lifetime of the allophycocyanin fluorescence is found to be about 4 ns using excitation pulses of low photon densities (10(13) photons.cm-2), but decreases to about 2 ns at higher photon densities. The relative quantum yield of the allophycocyanin fluorescence decreases almost 10 fold over the range of laser pulse intensities, 10(13)--10(16) photons-cm-2. Fluorescence quenching by exciton-exciton annihilation is only observed in allophycocyanin and could be a consequence of the long lifetime of the single exciton in this pigment.

Energy Transfer↗

PubMed1979

[Energy transfer from tryptophan to 1, N6-ethenoadenosine in frozen aqueous solution].

Mixed aggregates of tryptophan and 1, N6-ethenoadenosine (epsilon Ado) are formed in frozen aqueous solutions at 77 K. In these aggregates one observes a quenching of tryptophan fluorescence by small amounts of epsilon Ado together with a sensitized fluorescence of epsilon Ado. About 70 tryptophan molecules are able to transfer their energy to one epsilon Ado molecule.

Adenosine↗

PubMed1978

Biliprotein assemble in the disc-shaped phycobilisomes of Rhodella violacea. On the molecular composition of energy-transfering complexes (tripartite units) forming the periphery of the phycobilisome.

Heterogeneous complexes with a molecular weight of about 790000 containing B-phycoerythrin (Bangiales phycoerythrin) and C-phycocyanin (Cyanophyceae phycocyanin) in a molar pigment ratio of 2:1 were isolated from purified, dissociated phycobilisomes. Electron microscopical investigations revealed structures of three discs aggregated face to face with an apparent distance of 1.5 nm between each disc. Two discs may represent phycoerythrin and one phycocyanin. The complexes are structurally identical with tripartite units of the phycobilisome periphery. Fluorescence data confirmed the integrity of isolated tripartite units. Excitation at 546 nm gives a fluorescence maximum at 644 nm, indicating intermolecular transfer of excitation energy from phycoerythrin to phycocyanin. Comparative subunit analyses and spectral data suggested that no allophycocyanin is present. Cross-linking experiments gave evidence for a polar arrangement of phycocyanin within the complex. This pigment itself is an aggregate of two smaller molecules each having a molecular weight of about 140000. Tripartite units contain all the phycoerythrin and phycocyanin of the phycobilisome. On this basis, a phycobilisome model is proposed which combines the aspects of biliprotein distribution, energy transfer and fine structure.

Macromolecular Substances↗

PubMed1979

Energy transfer among the chromophores in phycocyanins measured by picosecond kinetics.

Energy-transfer processes in the algal light-harvesting proteins, the phycocyanins, have been studied by means of picosecond absorption spectroscopy. After excitation at 530 nm, the absorption at several wavelengths in the range 480--669 nm decayed with a short time constant (picosecond) and a long time constant (greater than 1 ns). For C-phycocyanin, energy transfer from the beta to the alpha subunits is interpreted as being a likely candidate for the short time constant; the long time constant probably is the excitation lifetime of the chromophore on the alpha subunits. The time constants for energy transfer in monomers, trimers, and hexamers of C-phycocyanin extracted from a blue-green alga, Phormidium luridum, were measured as approximately 85, approximately 56, and approximately 32 ps, respectively. The corresponding time constant in the cryptomonad phycocyanin 645 from Chroomonas species was found to be less than 5 ps.

Cyanobacteria↗

PubMed1978

Fluorescence energy-transfer studies on the pyruvate dehydrogenase complex isolated from Azotobacter vinelandii.

Fluorescence energy transfer has been employed to estimate the minimum distance between each of the active sites of the 4 component enzymes of the pyruvate dehydrogenase multienzyme complex from Azotobacter vinelandii. No energy transfer was seen between thiochrome diphosphate, bound to the pyruvate decarboxylase active site, and the FAD of the lipoamide dehydrogenase active site. Likewise, several fluorescent sulfhydryl labels, which were specifically bound to the lipoyl moiety of lipoyl transacetylase, showed no energy transfer to either the flavin or thiochrome diphosphate. These observations suggest that all the active centers of the complex are quite far apart (greater than or equal to 40 nm), at least during some stages of catalysis. These results do not preclude the possibility that the distances change during catalysis. Several of the fluorescent probes used possessed multiple fluorescent lifetimes, as shown by determination of lifetime averages by both phase and modulation measurements on a phase fluorimeter. These lifetimes are shown to result from multiple factors, not necessarily related to multiple protein conformations.

Acetylcysteine↗

PubMed1977

Fluorescence energy transfer between Ca2+ transport ATPase molecules in artificial membranes.

The purified ATPase of sarcoplasmic reticulum was covalently labeled with N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (1,5-IAEDANS) or with iodoacetamidofluorescein (IAF). In reconstituted vesicles containing both types of ATPase molecules fluorescence energy transfer was observed from the IAEDANS (donor) to the IAF (acceptor) fluorophore as determined by the ratio of donor and acceptor fluorescence intensities, and by nanosecond decay measurements of donor fluorescence in the presence or absence of the acceptor. The observed energy transfer may arise by random collisions between ATPase molecules due to Brownian motion or by formation of complexes containing several ATPase molecules. Experimental distinction between these two models of energy transfer is possible based on predictions derived from mathematical models. Up to tenfold dilution of the lipid phase of reconstituted vesicles with egg lecithin had no measurable effect upon the energy transfer, suggesting that random collision between ATPase molecules in the lipid phase is not the principal cause of the observed effect. Addition of unlabeled ATPase in five- to tenfold molar excess over the labeled molecules abolished energy transfer. These observations together with electron microscopic and chemical cross-linking studies support the existence of ATPase oligomers in the membrane with sufficiently long lifetimes for energy transfer to occur. A hypothetical equilibrium between monomeric and tetrameric forms of the ATPase governed by the membrane potential is proposed as the structural basis of the regulation of Ca uptake and release by sarcoplasmic reticulum membranes during muscle contraction and relaxation.

Adenosine Triphosphatases↗

PubMed1978

Structural studies on bacterial luciferase using energy transfer and emission anisotropy.

The distance between specific sites on bacterial luciferase was estimated by energy transfer. Luciferase was fluorescently labeled by reaction of an essential sulfhydryl group with N-(1-pyrene)maleimide and N-[p-(2-benzoxazolyl)phenyl]meleimide. Both of the modified enzymes bind 8-anilino-1-naphthalenesulfonate (Ans) with affinities similar to that exhibited by the native luciferase. Using each of the two fluorescent probes as a donor and the bound Ans as an acceptor, the energy transfer efficiencies were determined by the resulting enhancement of fluorescence of the acceptor. The corresponding distance was calculated to be in the range of 21 to 37 A. Energy-transfer studies were also carried out using fluorescence lifetime measurements of bound ANS, acting as a donor with bound FMN as an acceptor. The corresponding distance was calculated to be between 30 and 58 A. Using samples of luciferase:Ans complex and luciferase modified with N-(1-pyrene)maleimide, the rotational correlation time of the enzyme-dye conjugate as awhole was found to be 47 +/- 2 ns. The observed rotational correlation time is much longer than that calculated for luciferase assuming a spherical structure, thus indicating an elongated form for the luciferase-dye conjugate.

Anilino Naphthalenesulfonates↗

PubMed1977

Pulse fluorimetry study of energy transfers between tryptophan residues and NADPH in beef liver glutamate dehydrogenase complexes.

A method is proposed to determine the rates of singlet energy transfers in an array of chromophores containing a finite number of donors and fluorescent acceptors. This method is based on measurements of transfer efficiency coupled with pulse fluorimetry. Three classes of donors can be distinguished which differ in their energy transfer rate. The rates of the first, the second and the third class are respectively greater than, of the order of, and smaller than the emission rate. The method is applied to the study of the energy transfers from tryptophan residues to NADPH, in ternary and quaternary glutamate dehydrogenase complexes. Practically, all these tryptophan residues belong to the first class. They can be divided into two subclasses having different transfer rate values. The distance between these residues and the NADPH site are of the order of 2.5 nm. In addition, the ligand binding induces a protein conformation change, leading to a fluorescence quenching of the tryptophanyl emission.

Chemical Phenomena↗

PubMed1979

Quaternary structure of DNA-dependent RNA polymerase from Escherichia coli. Measurement of distances by fluorescence energy transfer.

Distances between the subunits in Escherichia coli RNA polymerase (core and holo enzyme) and the rifamycin binding site have been determined using the nonradiative energy transfer technique. The appropriate donor and acceptor labels have been chosen in order to optimize the spectral overlap and maximize the energy transfer. Spacer linked derivatives of rifamycin SV possessing nitrobenzo-oxadiazole groups (energy acceptor) were synthesized for this purpose. The donor label, acetylaminoethylaminonaphthalene sulfonate, was introduced into the intact enzyme, and the subunits were separated. Enzyme molecules selectively labelled on one kind of subunit were produced by mixed reconstitution techniques employing labelled and non labelled subunits. The labelled beta'-subunit could not be prepared in sufficient amounts. Energy transfer distances between the enzyme-bound rifamycin derivative and the subunits were determined to be approximately 5.9 nm for sigma, 7.2 nm for alpha 2 and 6.1 nm for beta.

Chemical Phenomena↗

PubMed1979

Location of the stilbenedisulfonate binding site of the human erythrocyte anion-exchange system by resonance energy transfer.

The stilbenedisulfonate inhibitory site of the human erythrocyte anion-exchange system has been characterized by using serveral fluorescent stilbenedisulfonates. The covalent inhibitor 4-benzamido-4'-isothiocyanostilbene-2,2'-disulfonate (BIDS) reacts specifically with the band 3 protein of the plasma membrane when added to intact erythrocytes, and the reversible inhibitors 4,4'-dibenzamidostilbene-2,2'-disulfonate (DBDS) and 4-benzamido-4'-aminostilbene-2,2'-disulfonate (BADS) show a fluorescence enhancement upon binding to the inhibitory site on erythrocyte ghosts. The fluorescence properties of all three bound probes indicate a rigid, hydrophobic site with nearby tryptophan residues. The Triton X-100 solublized and purified band 3 protein has similar affinities for DBDS, BADS, and 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS) to those observed on intact erythrocytes and erythrocyte ghosts, showing that the anion binding site is not perturbed by the solubilization procedure. The distance between the stilbenedisulfonate binding site and a group of cysteine residues on the 40 000-dalton amino-terminal cytoplasmic domain of band 3 was measured by the fluorescence resonance energy transfer technique. Four different fluorescent sulfhydryl reagents were used as either energy transfer donors or energy transfer acceptors in combination with the stilbenedisulfonates (BIDS, DBDS, BADS, and DNDS). Efficiencies of transfer were measured by sensitized emisssion, donor quenching, and donor lifetime changes. Although these sites are approachable from opposite sides of the membrane by impermeant reagents, they are separated by only 34--42 A, indicating that the anion binding site is located in a protein cleft which extends some distance into the membrane.

Energy Transfer↗

PubMedDate not supplied

Energy transfer and its dependence on membrane properties.

With isolated chloroplasts variations in the degree of energy transfer between light-harvesting chlorophyll-protein complexes can be induced by changing the cation content of the suspending medium. The changes can be observed by measuring chlorophyll-fluorescence yields and lifetimes and are probably brought about by conformatial changes in the thylakoid membrane. Detailed studies of the properties of cation-induced changes in chlorophyll fluorescence indicated that the alterations in pigment organization are due to variations in the density of positive charges immediately adjacent to the surface of the thylakoid membrane, being in qualitative agreement with predictions based on the Gouy-Chapman theory of diffuse double layers. Possible mechanisms for the membrane structural changes controlling energy transfer are given.

Chlorophyll↗

PubMed1979

Comparison of fluorescence energy transfer and quenching methods to establish the position and orientation of components within the transverse plane of the lipid bilayer. Application to the gramicidin A--bilayer interaction.

Fluorescence quenching and resonance energy transfer methods have been used to investigate the position of fluorophores in the lateral and transverse planes of the lipid bilayer. A series of n-(9-anthroyloxy) fatty acids (n = 2, 6, 9, and 12) have been used as energy-transfer acceptors so that apparent transfer distances from a membrane-bound donor (N-stearoyltryptophan) have a transverse as well as a lateral component. Both theory and experiment show that the energy-transfer method is not precise enough to discriminate between the positions of the fluorophores in the transverse plane of the bilayer. The n-(9-anthroyloxy) fatty acids are also susceptible to quenching by the indole moiety of tryptophan. The relative quenching efficiency can provide a semiquantitative measure of the position of quenching molecules in the lipid bilayer. The quenching techniques are applied to the determination of the orientation of gramicidin A in lipid bilayers. The tryptophan residues of gramicidin appear to be located near the membrane surface in agreement with the head-to-head dimeric structure proposed by D. W. Urry et al. [(1971) Proc. Natl. Acad. Sci. U.S.A. 68, 672--676].

Energy Transfer↗

PubMed1978

Excitation energy transfer between pigment system II units in blue-green algae.

Efficiency in excitation energy transfer from closed to open reaction center II in blue-green and red algae was estimated by the method developed by Joliot and Joliot (C.R. Acad. Sci. (1964) 258, 4622--4625) after slight modification; the number of open reaction centers II was counted from the mean O2 yield of repetitive short flashes. The efficiency in energy transfer in Chlorella pyrenoidosa was the same in our measurement as that reported by Joliot and Joliot (0.55 +/- 0.02). However, the values obtained with four blue-green algae and one red alga were very small, in a range of 0.00--0.07. The low efficiency was always obtained independently of the size of the apparent photosynthetic unit which was varied by growth conditions. Results indicated that pigment system II forms a unit in which only one reaction center II is operative.

Cyanobacteria↗

PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga.

The wavelength-resolved fluorescence emission kinetics of the accessory pigments and chlorophyll a in Porphyridium cruentum have been studied by pico-second laser spectroscopy. Direct excitation of the pigment B-phycoerythrin with a 530 nm, 6 ps pulse produced fluorescence emission from all of the pigments as a result of energy transfer between the pigments to the reaction centre of Photosystem II. The emission from B-phycoerythrin at 576 nm follows a nonexponential decay law with a mean fluorescence lifetime of 70 ps, whereas the fluorescence from R-phycocyanin (640 nm), allophycocyanin (660 nm) and chlorophyll a (685 nm) all appeared to follow an exponential decay law with lifetimes of 90 ps, 118 ps and 175 ps respectively. Upon closure of the Photosystem II reaction centres with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination the chlorophyll a decay became non-exponential, having a long component with an apparent lifetime of 840 ps. The fluorescence from the latter three pigments all showed finite risetimes to the maximum emission intensity of 12 ps for R-phycocyanin, 24 ps for allophycocyanin and 50 ps for chlorophyll a. A kinetic analysis of these results indicates that energy transfer between the pigments is at least 99% efficient and is governed by an exp --At1/2 transfer function. The apparent exponential behaviour of the fluorescence decay functions of the latter three pigments is shown to be a direct result of the energy transfer kinetics, as are the observed risetimes in the fluorescence emissions.

Chlorophyll↗

PubMed1979

The reconstitution of energy transfer in membranes from a bacteriochlorophyll-less mutant of Rhodopseudomonas sphaeroides by addition of light-harvesting and reaction centre pigment-protein complexes.

Antenna and reaction centre complexes purified from photosynthetically-grown cells of Rhodopseudomonas sphaeroides have been mixed with cytoplasmic membranes prepared from an aerobically-grown bacteriochlorophyll-less mutant of Rp. sphaeroides (designated 01) in the presence of 1% sodium cholate. After removal of the cholate by dislysis, the dislysate was subjected to isopycnic centrifugation. Reconstituted cytochrome c2 photooxidation and cytochrome b photoreduction was demonstrated in a pigmented fraction recovered from the sucrose gradient, suggesting that the pigment-proteins were incorporated into the 01 membrane. The fluorescence properties of the system were examined. The appearance of a variable component after the initial fast fluorescence rise indicated that energy transfer occurred between the antenna and reaction centre proteins in the presence of 01 membrane. The order in which the system was assembled was important. Reconstituted energy transfer with a pre-dialysed reaction centre-antenna complex was more effective than when all the components were mixed at once. Energy transfer was also reconstituted between added reaction centre protein and the endogenous antenna present in membranes from the pigmented, but aerobically-grown reaction centre-less mutant PM8dp of Rp. sphaeroides. Preparations of 01 membranes reconstituted with reaction centre exhibited a light intensity dependent cytochrome c2 photooxidation. At low exciting light intensities, preparations containing reconstituted antenna protein in addition to reaction centres showed greated membrane cytochrome c2 photooxidation than preparations with the antenna omitted; this improvement was maximal when a pre-dialysed antenna-reaction centre complex was used.

Aerobiosis↗

PubMed1978

Energy transfer in the purple membrane of Halobacterium halobium.

The absorption spectrum of the primary photoproduct (the bathoproduct, or K) of the purple membrane protein (PM) at-196 degrees C has a maximum at 628 nm and an extinction coefficient of 87,000. Knowing the absorption spectrum allowed us to calculate the quantum efficiencies for PM to K and K to PM conversion at -196 degrees C. Direct measurements of these quantum yeilds at -196 degrees C gave 0.33 +/- 0.05 and 0.67 +/- 0.04, respectively. Determination of relative quantum efficiencies for PM to K and K to PM conversion by analysis of the absorption spectra of several photostationary-state mixtures of PM and K at -196 degrees C, however, gave wavelength-dependent quantum efficiencies that appear to be greater than 1. These anomolous results can be readily explained in terms of energy transfer from PM to K within the trimer clusters of pigment molecules which exist in the purple membrane. A model for such a transfer predicts an efficiency of energy transfer from PM to K of about 43%.

Bacteriorhodopsins↗