Kinetics of triplet-triplet energy transfer and intramolecular distances in enzyme-inhibitor complexes.
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Binding Sites↗
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[Relationship between the lifetime and energy of the triplet states of chlorophylls. Measurement of the energy of the triplet state of bacteriochlorophyll and bacteriopheophytin a].
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Bacteriochlorophylls↗
Quenching of fluorescence by triplet excited states in chloroplasts.
The fluorescence quantum yield in spinach chloroplasts at room temperature has been studied utilizing a 0.5-4.0 mus duration dye laser flash of varying intensities as an excitation source. The yield (phi) and carotenoid triplet concentration were monitored both during and following the laser flash. The triplet concentration was monitored by transient absorption spectoscopy at 515 nm, while the yield phi following the laser was probed with a low intensity xenon flash. The fluorescence is quenched by factors of up to 10-12, depending on the intensity of the flash and the time interval following the onset of the flash. This quenching is attributed to a quencher Q whose concentration is denoted by Q. The relative instantaneous concentration of Q was calculated from phi utilizing the Stern-Volmer equation, and its buildup and decay kinetics were compared to those of carotenoid triplets. At high flash intensities (greater than 10(16) photon . cm-2) the decay kinetics of Q are slower than those of the carotenoid triplets, while at lower flash intensities they are similar. Q is sensitive to oxygen and it is proposed that Q, at the higher intensities, is a trapped chlorophyll triplet. This hypothesis accounts well for the continuing rise of the carotenoid triplet concentration for 1-2 mus after the cessation of the laser pulse by a slow detrapping mechanism, and the subsequent capture of the triplet energy by carotenoid molecules. At the maximum laser intensities, the carotenoid triplet concentration is about one per 100 chlorophyll molecules. The maximum chlorophyll ion concentration generated by the laser pulses was estimated to be below 0.8 ions/100 chlorophyll molecules. None of the observations described here were altered when a picosecond pulse laser train was substituted for the microsecond pulse. A simple kinetic model describing the generation of singlets and triplets (by intersystem crossing), and their subsequent interaction leading to fluorescence quenching, accounts well for the observations. The two coupled differential equations describing the time dependent evolution of singlet and triplet excited states are solved numerically. Using a single-triplet bimolecular rate constant of gammast = 10(-8) cm3 . s-1, the following observations can be accounted for: (1) the rapid initial drop in phi and its subsequent levelling off with increasing time during the laser pulse, (2) the buildup of the triplets during the pulse, and (3) the integrated yield of triplets per pulse as a function of the energy of the flash.
Carotenoids↗
[Quantitative comparison of ribosome binding sites of twelve nucleotide sequences from Escherichia coli (RNA- and DNA phages) based on triplet patterns (author's transl)].
The molecular structure of ribosome binding sites of ten phage genes and two messengers of Escherichia coli were compared concerning the signation parts which are presumably used by ribosomes for recognition and binding. With a simple calculation based on triplet patterns sofar unknown agreements between all of these sequences were found. In several cases it was shown that agreements between old sequences are easier recognizable if the purine- and pyrimidine bases are put into the triplets instead of the four A, G, C, and U (T) bases. In such cases "homologous" parts of sequences were recognized with more distinctness. This is true in our case for the double triplet (hexaplet) py-pu-pu-pu-pu-(pu) and the binding site triplet py-pu-pu, which are preceding the initiator. These triplets are in specific positions in all twelve sequences which were compared. The different course of the quaternary and the binary conformity curves (diagram 1) may show for the investigated area that the RNA phage gene-part is organized according to the well known quaternary triplet code. On the contrary the phage phi-gene-part seems to be organized according to a more simple, binary triplet sequence of purine and pyrimidine bases. The binary sequence seems to be the more original, the quaternary the derived one.
Base Sequence↗
Further evidence for dissipative energy migration via triplet states in photosynthesis. The protective mechanism of carotenoids in Rhodopseudomonas spheroides chromatophores.
The protection action of carotenoids against irreversible photodestruction was discovered in photosynthetic bacteria by Stanieda and coworkers. In green plant material it was found by Wolff and Witt (1969) Z. Naturforsch, 24b, 1031-1037 and (1972) Proc. 2nd. Int. Congr. Photosynthesis Res. Stresa (Forti, G., Avron, M. and Melandri, A., eds.), Vol. 2, pp. 931-936, Dr. W. Junk, N. V. Publ. The Hague) that the formation of special carotenoid triplet states (via very rapid energy transfer from excited chlorophylls) and their fast radiationless decay in tau1/2 approximately 3 microns is at least one mechanism for the protective action of carotenoids to irreversible photooxidation of the chlorophylls. Hence, it is anticipated that the same mechanism might be realized also in bacteria. The present study gives evidence for such a "triplet valve" to be established also in bacteria. This conclusion was derived from the following observations: 1. The light-induced difference spectrum shows a bleaching of a carotenoid at three characteristic wavelength between 400 and 500 nm. A positive peak around 533 nm indicates the formation of a carotenoid triplet state. 2. The absorption changes can be induced by red light which excites only bacteriochlorophyll. This indicates an energy transfer from bacteriochlorophyll to carotenoids. 3. The light-induced carotenoid triplets decay radiationless in 3 microns in air-saturated aqueous suspensions of the chromatophores. 4. The carotenoid triplet formation occurs only at actinic flash intensities where the photosynthesis becomes saturated. 5. Addition of dithionite, which blocks photosynthesis, markedly increases the extent of carotenoid triplet formation. The different types of exciton migration within the photosynthetic unit are discussed, especially the routes leading to the dissipation of excess excitation energy.
Bacterial Chromatophores↗
Monozygotic triplets with discordance for diabetes mellitus and diabetic microangiopathy.
A set of monozygotic triplets (PE.K., P.K., S.K.) has been studied. There is no diabetes in first-degree relatives. PE.K. developed insulin-requiring (60 U. NPH) diabetes at the age of 13 years. Over a period of 11 years since that time, numerous studies of insulin and growth-hormone secretion were performed on P.K. and S.K., including multiple oral glucose tolerance tests (OGTTs), cortisone-primed oral glucose tolerance tests (C-OGTTs), intravenous glucose tolerance tests (IVGTTs), and intravenous tolbutamide tests (IVTTs). The results of each test were compared with age- and sex-matched control subjects. P. K. developed insulin-requiring (56 U. NPH) diabetes after remaining discordant for eight years. Glucose, insilin, and growth-hormone responses during all tests were normal except during the IVGTT performed four months prior to the onset of diabetes. This last IVGTT revealed a glucose disappearance rate of 0.98 per cent per minute, and the slope of the regression line of serum-insulin response (IRI) on blood glucose (BG) was markedly decreased to 0.005 micronU./ml. IRI/mg./dl. BG (controls 0.340 +/- 0.04; mean +/- S.E.M.). The insulin responses in P.K. and S.K. were similar during all OGTTs, C-OGTTs, and IVTTs. S.K. has continued to maintain normal glucose tolerance and normal insulin and growth-hormone responses during all tests. The histocompability antigen studies have revealed HLA-A2, AW24, BW15, and BW40 phenotype in these monozygotic triplets. Muscle capillary basement membranes of the nondiabetic triplet were normal, whereas both diabetic triplets manifested evidence of capillary basement membrane thickening. The clinical and biochemical profiles in these triplets and the capillary basement membrane data lend strong credence to the role of "nongenetic" determinants in the development of "genetic" diabetes as well as diabetic microangiopathy in juvenile-onset-type diabetes.
Adolescent↗
[The use of partusisten in the delivery of triplets with an incarcerated fetus (author's transl)].
A triplet delivery is reported. The multiple pregnancy was undiagnosed prior to labor. Twins were diagnosed on admission for delivery. The ultrasonic and abdominal EKG findings at term are discussed. The hitherto undiagnosed third triplet became incarcerated following the administration of two units of syntocinon after the delivery of the second triplet. The intrapartum tocolysis with partusisten became life saving for the third triplet on three counts. 1. The progressive acidosis was stopped. 2. Time was gained to prepared for delivery of the last triplet. 3. Internal podalic version and extraction was much easier.
Diagnostic Errors↗
Bacteriochlorophyll fluorescence of purple bacteria at low redox potentials. The relationship between reaction center triplet yield and the emission yield.
This work describes fluorescence yield measurements in suspensions of strains of Rhodospirillum rubrum and Rhodopseudomonas sphaeroides in which the iron . quinone complex (X) was chemically reduced (state [PIX-]; P is the reaction center bacteriochlorophyll dimer, I is the long wavelength bacteriopheophytin), and compares these with the fluorescence observed when all the traps are open (state [PIX]) and with the fluorescence observed when all the traps are closed (state [P+IX]). At 77 K the amplitude and the shape of the fluorescence emission spectrum in [PIX-] are identical to those observed in [PIX]. This is a strong indication that all the extra fluorescence observed at room temperature in [PIX-] is, in fact, caused by an efficient back reaction [P+I-X-] leads to [P*IX-]. Using an equation similar to the original Vredenberg-Duysens relationship (Vredenburg, W.J. and Duysens, L.N.M. (1963) Nature 197, 355-357) but now assuming that a single reaction center has a probability pt of trapping an excitation and (1--pt) of re-emitting it to the surroundings, we are able to calculate pt as a function of the temperature by measuring the fluorescence in [PIX], [PIX-] and [P+IX] as a function of the temperature. The calculated pt values agree reasonably well with triplet yields measured in isolated reaction centers. Finally, we have measured the reaction center triplet yield (PTR) in intact systems and we have shown that the sum of the triplet yield and the remaining loss processes (PL) in the antenna bacteriochlorophyll including the bacteriochlorophyll dimer (such as fluorescence, internal conversion or direct triplet formation) is approximately constant; if we assume that at 77 K the only process which occurs in the reaction center is the formation of a reaction center triplet, than PTR + PL=1. The energy barrier between [P*IX-] and [P+I-X-] was estimated to be 0.11--0.15 eV for a set of preparations.
Bacteriochlorophylls↗
Magnetophotoselection of the triplet state of reaction centers from Rhodopseudomonas sphaeroides R-26.
Reaction centers of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26, give rise to large triplet state EPR signals upon illumination at low temperature (11 K). Utilizing monochromatic polarized light to generate the EPR spectra (magnetophotoselection) we have shown that the intensities of the observed triplet signals are strongly dependent upon the wavelength and polarization direction of the excitation. These data can be used to calculate the orientations of the excited transition moments with respect to each other and with respect to the triplet state principal magnetic axes system. Our quantitative approach is to follow the procedure outlined in a previous publication (Frank, H.A., Friesner, R., Nairn, J.A., Dismukes, G.C. and Sauer, K. (1979) Biochim. Biophys. Acta 547, 484-501) where computer simulations of the observed triplet state spectra were employed. The results presented in the present work indicate that the transition moment at 870 nm which is associated with the bacteriochlorophyll 'special pair' lies almost entirely along one of the principal magnetic axes of the triplet state. Aso, the 870 nm transition moment makes an angle of approx. 60 degrees with the 546 nm transition moment which is associated with a bacteriopheophytin. This latter result is in agreement with previous photoselection studies on the same bacterial species (Vermeglio, A., Breton, J., Paillotin, G. and Cogdell, R. (1978) Biochim. Biophys. Acta 501, 514-530).
Bacterial Chromatophores↗
Flash photolysis of human serum albumin: characterization of the indole triplet absorption spectrum and decay at ambient temperature.
The method of flash photolysis was used to identify the transient absorption spectrum and to characterize the decay kinetics of the indole triplet of human serum albumin. This protein was studied because it contains a single indole side chain which is deeply buried in an expandable oily region and because the phosphorescence of the homologous indole in bovine serum albumin could not be detected at ambient temperatures. The transient was identified on the following basis: (i) its triplet-triplet absorption spectrum was similar to those previously reported for indole and tryptophan; (ii) it was quenched by small quantities of oxygen; and (iii) it was photobleached by 370- to 700-nm light. In a nitrogen-saturated solution at room temperature, the indole triplet decays exponentially for more than a factor of 10 with a lifetime of 0.5 msec. These observations suggest that, because of its exponential decay and relatively long lifetime, the triplet will be more valuable than the indole singlet as an intrinsic reporter group for the study of the structure and dynamics of proteins in solution.
Humans↗
[Investigation of the microstructure of biological systems by triplet label].
A method for investigating the microstruct and dynamics of biological systems by means of triplet-excited molecules is suggested. The method is based on the phenomenon of triplet excitation disactivation by exchange-resonance triplet-triplet energy transfer to the acceptor or by intercombination conversion induced by interaction of an excited molecule with a paramagnetic center. The disactivation efficiency was measured by registrating the phosphorescense decay kinetics. The interaction of the triplet label eosin isothiocyanate, covalently coupled with albumine, lysozyme, sarcoplasmic reticulum membrane and Ca-Mg-dependent sarcoplasmic reticulum ATPase, with O2, the stable nitroxide radicals and ions of Mn2+ was investigated to analyse the potentialities of this method. As a model system the eosin phosphorescence quenching by the same quenchers in glycerine-aguaous solutions was studied. The method permits to investigate the microviscosity and microstructure of biological objects in the label attached region on interaction of the label with a sound-quencher with constants being 10(4) divided by 10(9) M-1 sec-1 and to measure the lateral diffusion of molecules in highly viscosity media (10 divided by 10(5) santypuas).
Adenosine Triphosphatases↗
Down syndrome in two of three triplets.
This is the first report to our knowledge of trisomy 21 in two members of a set of triplets. The two with Down syndrome are monozygous; the other triplet is not identical. These triplets were born to a 22-year-old woman in whose family there have been six sets of twins (four like-sex) since 1775. Neither parent has any chromosomal abnormality. Zygosity estimates in the triplets are derived from studies of red blood cell antigens and HLA typing. Twinning has been reported in association with many different chromosome abnormalities. It has been suggested that the incidence of Down syndrome among twins is significantly higher than among singletons. It seems likely that some families have a heritable predisposition to both twinning and chromosome abnormalities.
Chromosome Banding↗
Triplet state population study in relation to the aggregation of proflavine in frozen solutions.
The evolution of the proflavine triplet state population with the extent of aggregation is examines, by ESRmeasurements, as a function of organic solvents and mineral salts, well known for their ability to influence the aggregation process. The intensity of the triplet state population has also been investigated as a function of pH. The insertion of aromatic molecules like DNA's nucleotides between dye molecules is shown to increase the intensity of the triplet state. It is put forward that the observed triplet state is characteristic of the singly protonated proflavine which seems to be the active species in in vivo experiments.
Acridines↗
Carotenoid triplet states in reaction centers from Rhodopseudomonas sphaeroides and Rhodospirillum rubrum.
Purified photochemical reaction centers from three strains of Rhodopseudomonas sphaeroides and two of Rhodospirillium rubrum were reduced with Na2S2O4 so as to block their photochemical electron transfer reactions. They then were excited with flashes lasting 5-30 ns. In all cases, absorbance measurements showed that the flash caused the immediate formation of a transient state (PF) which had been detected previously in reaction centers from Rps. sphaeroides strain R26. Previous work has shown that state PF is an intermediate in the photochemical electron transfer reaction in the reaction centers of that particular strain, and the present work generalizes that conclusion. In the reaction centers from two strains that lack carotenoids (Rps. sphaeroides R26 and R. rubrum G9), the decay of PF yields a longer-lived state (PR) which is probably a triplet state of the bacteriochlorophyll of the reaction center. In the R26 preparation, the decay of PF was found to have a half-time of 10 +/- 2 ns. The decay kinetics rule out the identification of PF as the fluorescent excited singlet state of the reaction center. In the reaction centers from three strains that contain carotenoids (Rps sphaeroides 2.4.1 and Ga, and R. rubrum S1), state PR was not detected, and the decay of PF generated triplet states of carotenoids. The efficiency of the coupling between the decay of PF and the formation of the carotenoid triplet appeared to be close to 100% at room temperature, but somewhat lower at 77 degrees K. Taken with previous results, this suggests that the coupling is direct and does not require the intermediate formation of state PR. This conclusion would be consistent with the view that PF is a biradical which can be triplet in character.
Carotenoids↗
Electron spin resonance in zero magnetic field of the reaction center triplet of photosynthetic bacteria.
The decay rates kx, ky, kz of the individual spin levels of the light-induced triplet state have been accurately measured by the zero-field resonance technique under conditions of very low light intensity and a microwave sweep rate of 2.5 MHz/microseconds, which is in excess of that commonly used in optical detection magnetic resonance experiments. The rates ku found correspond well with those previously determined under somewhat different conditions (Hoff, A.J. (1976) Biochim. Biophys. Acta 440, 765--771) and with those inferred from the decay at 4.2 degrees K of the triplet-triplet absorption after picosecond excitation (Parson, W.W. and Monger, T.G. (1977) Brookhaven Symp. Biology 28, 195--212). Thus there seems no reason to doubt that PR corresponds to the triplet state detected by ESR. In a recent publication Clarke and Connors (Clarke, R.H. and Conners, R.E. (1976) Chem. Phys. Lett. 42, 69--72) published values of the rates ku which differ substantially from ours and which lead to a mean lifetime in excess of that of PR. We show that erroneous rates are obtained when the microwave sweep rate is not made fast relative to the decay of the individual spin levels. Zero-field splitting parameters for a member of photosynthetic bacteria have been measured with an accuracy of better than 0.4% for D and 1% for E. The enhanced precision as compared to conventional ESR allows one to discriminate between species of one family. Deuteration reduces the ku values by a factor of about 2, with little spin selectivity. This effect is much larger than previously observed for chlorophyll a. The present results explain the decrease in fluorescence intensity observed on microwave saturation in zero-field optical detection magnetic resonance experiments, and they also show that the simple exciton model is inadequate to derive the geometry of the reaction center dimer from the observed zerofield splitting and decay rates.
Electron Spin Resonance Spectroscopy↗
Orientation of the bacteriochlorophyll triplet and the primary ubiquinone acceptor of Rhodospirillum rubrum in membrane multilayers determined by ESR spectroscopy (I).
Chromatophores from Rhodospirillum rubrum were oriented as multilayers on quartz slides under reducing conditions. Irradiation of these multilayers in the resonance cavity of an ESR spectrometer at 6 K yielded the spectrum of the bacteriochlorophyll dimer triplet. The relative intesities of the main six lines of the triplet were dependent on the angle subtended by the direction of the external magnetic field with plane of the multilayers. The angular dependence of the intensities of these transitions can best be interpreted in terms of one of the principal axes of the triplet lying along the plane of the membrane while the other two axes are titled 10--20 degrees away from the parallel to and normal to the membrane directions. If we assume the porphyrin planes of the dimer to be parallel and the largest splitting of the triplet transitions to correspond to those transitions in a direction normal to this plane, then these data imply that the dimer planes are nearly perpendicular to the membrane plane. Purified iron-depleted phototrap complexes were similarly oriented in reconstituted phosphatidylcholine multilayers and the angular dependence of the light-induced spectrum recorded at room temperature. A computer analysis of this angular dependence suggests that the plane of the primary ubiquinone acceptor molecule is parallel to the plane of the membrane and therefore perpendicular to the donor.
Bacterial Chromatophores↗
A laser flash photolysis study of the reactivities of the triplet states of 8-methoxypsoralen and 4,5',8-trimethylpsoralen with nucleic acid bases in solution.
The extinction coefficients, quantum yields and reactivities of the triplet states of 8-methoxypsoralen and 4,5',8-trimethylpsoralen in methanolic solution have been determined using laser flash photolysis techniques. The second-order rate constants for the quenching of these triplet states by pyrimidine and purine bases were found to be several orders of magnitude lower than those found for other furocoumarin derivatives. This may suggest, therefore, that the skin photosensitising ability of such compounds does not necessarily correlate with in vitro triplet state reactivity. Preliminary experiments on the reactivity of the psoralen triplet state with DNA itself indicate that no transient absorptions due to psoralen excited states can be observed when a photon is absorbed by the psoralen-DNA complex.
Carotenoids↗
Effect of stacking interactions with poly(riboadenylic acid) on the triplet state properties of tryptophan.
Optically detected magnetic resonance (ODMR) signals of tryptophan (Trp) have been measured in L-lysyl-L-tryptophyl-L-lysine (Lys-Trp-Lys) and in its complex with poly(riboadenylic acid) [poly(rA)]. Measurements were made with optical narrow band detection through the Trp O-O band. Plots of [D] and [E] vs. lambda are distinctly different for Lys-Trp-Lys and its complex with poly(rA). A reduction of [D], in particular, is consistent with stacking of Trp with adenine in the complex, since this effect is expected from charge-transfer contributions in the excited triplet state. Triplet energy transfer from poly(rA) to Lys-Trp-Lys is nearly complete at 77 K, with a Trp:adenine ratio of 0.1. The energy transfer efficiency is considerably reduced at 4.2 K and below, probably resulting from reduction of the triplet mobility in the polymer. Analysis of the phosphorescence decays shows that the triplet states of poly(rA), Lys-Trp-Lys, and their complex decay nonexponentially. Binding of polylysine to poly(rA) has no effect on the phosphorescence spectrum, but the decay kinetics are changed.
Luminescent Measurements↗