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At least 19 recordsLinked to original sources
PubMed1976

The study of the primary photoprocesses in photosystem I of chloroplasts. Recombination luminescence, chlorophyll triplet state and triplet-triplet annihilation.

The dependence of the delayed luminescence of Photosystem I on the state of the reaction centers has been studied. Light flash induces a charge separation in the centers: P-700-P-430 hv in equilibrium P-700+-P-430-. Dark recombination of charges is accompanied by the recombination luminescence with tau1/2 congruent to 20ms. If the centers are in the P-700-P-430- state or if P-430 is inactivated by heat, then flashing of Photosystem I generates the triplet state chlorophyll with tau1/2 congruent to 0.5 ms. The triplet state has been measured by the delayed fluorescence of chlorophyll at 20 degrees C and 77 degrees K and by the chlorophyll phosphorescence at 77 degrees K. The delayed fluorescence at 20 degrees C arises from the thermal activation of the triplet state up to the excited singlet level of chlorophyll and at 77 degrees K it is due to triplet-triplet annihilation. The quantum yield of the triplet formation, estimated by a comparison of the light saturation curves of delayed fluorescence at 20 degrees C and of P-700 photooxidation under the same experimental (optical) conditions, is approximately 0.9 of the P-700+ yield. Only one triplet of chlorophyll can be generated per P-700. Under heat inactivation of P-430 the triplet formation is not observed when P-700 is oxidized. It is assumed that the triplet-triplet annihilation at 77 degrees K is related with the strong interaction between the chlorophyll molecules in the pigment complex of Photosystem I. The possibility of a triplet participation in the primary processes of photosynthesis is discussed.

Chlorophyll↗
PubMed1976

Triplet states of bacteriochlorophyll and carotenoids in chromatophores of photosynthetic bacteria.

Chromatophores from photosynthetic bacteria were excited with flashes lasting approx. 15 ns. Transient optical absorbance changes not associated with the photochemical electron-transfer reactions were interpreted as reflecting the conversion of bacteriochlorophyll or carotenoids into triplet states. Triplet states of various carotenoids were detected in five strains of bacteria; triplet states of bacteriochlorophyll, in two strains that lack carotenoids. Triplet states of antenna pigments could be distinguished from those of pigments specifically associated with the photochemical reaction centers. Antenna pigments were converted into their triplet states if the photochemical apparatus was oversaturated with light, if the primary photochemical reaction was blocked by prior chemical oxidation of P-870 or reduction of the primary electron acceptor, or if the bacteria were genetically devoid of reaction centers. Only the reduction of the electron acceptor appeared to lead to the formation of triplet states in the reaction centers. In the antenna bacteriochlorophyll, triplet states probably arise from excited singlet states by intersystem crossing. The antenna carotenoid triplets probably are formed by energy transfer from triplet antenna bacteriochlorophyll. The energy transfer process has a half time of approx. 20 ns, and is about 1 X 10(3) times more rapid than the reaction of the bacteriochlorophyll triplet states with O2. This is consistent with a role of carotenoids in preventing the formation of singlet O2 in vivo. In the absence of carotenoids and O2, they decay half times of the triplet states are 70 mus for the antenna bacteriochlorophyll and 6-10 mus for the reaction center bacteriochlorophyll. The carotenoid triplets decay with half times of 2-8 mus. With eak flashes, the quantum yields of the antenna triplet states are in the order of 0.02. The quantum yields decline severely after approximately one triplet state is formed per photosynthetic unit, so that even extremely strong flashes convert only a very small fraction of the antenna pigments into triplet states. The yield of fluorescence from the antenna bacteriochlorophyll declines similarly. These observations can be explained by the proposal that single-triplet fusion causes rapid quenching of excited single states in the antenna bacteriochlorophyll.

Bacterial Chromatophores↗
PubMed1979

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↗
PubMedDate not supplied

Reduction of soft tissue deposition in normal triplets.

In a previous study, birth weight projections obtained with Rossavik growth models were systematically greater than actual birth weights in triplets but not in singletons. To investigate the cause of this overestimation, average mean percent deviations for head circumference (HC), abdominal circumference (AC), thigh circumference (ThC), and weight (WT) at different times in the third trimester were studied in 13 normal triplet and 20 normal singleton fetuses using individual growth curve standards. Average mean percent deviation values for HC in both singletons and triplets were close to zero throughout the third trimester. Average mean percent deviation values for AC in both singletons and triplets were similar, and remained relatively constant. Average mean percent deviation values for ThC in triplets decreased toward the end of the third trimester, but those for singletons increased. Average mean percent deviation values for estimated weight did not change during the third trimester in singletons whereas those in triplets decreased. The difference in average mean percent deviation values for estimated weight between singletons and triplets in the 32- to 36-week interval was statistically significant. There were no significant differences between actual and predicted measurements for HC in both singletons and triplets at birth. However, actual birth measurements were systematically less than predicted birth measurements for AC and ThC in singletons, and for AC, ThC, and WT for triplets. These systematic differences were significantly larger in triplets for ThC and WT. Nutrition Score values, direct measures of subcutaneous tissue, were significantly lower in triplets compared to singletons.(ABSTRACT TRUNCATED AT 250 WORDS)

Birth Weight↗
PubMed1992

Spectroscopic characterization of triplet forming states in photosystem II.

Fluorescence and electron paramagnetic resonance (EPR) measurements have been applied to characterize chlorophyll triplet formation in the reaction center of photosystem II (PSII). A highly triplet forming state was generated in PSII membranes by chemical double reduction of the primary electron acceptor QA. In triplet forming PSII centers, the steady-state yield of chlorophyll fluorescence decreased to about 70% of the maximal fluorescence yield observed in closed PSII centers in which QA is singly reduced. The results are well interpreted in the framework of a model where the charge state of QA electrostatically controls the yield of primary charge separation [Schatz, G. H., Brock, H., & Holzwarth, A. R. (1988) Biophys. J. 54, 397-405]. Thus, high triplet yield and decreased, although still quite high, fluorescence indicate a charge-neutralized state of PSII in which QA is singly or doubly reduced and protonated or absent. The EPR signal of the triplet primary chlorophyll donor, 3P680, is suppressed by illumination at 77 K concomitant with the formation of a cationic radical (g = 2.0025-2.0027, and 0.92 mT wide) that is stable in the dark. This is attributed to the oxidation of an accessory chlorophyll (Chl) in the vicinity of P680. Electrostatic repulsion between Chl+ and P680+ is likely to prevent primary charge separation, and in turn triplet formation, providing a further example of electrostatic control of primary charge separation. The triplet P680 EPR signal is also suppressed in the presence of oxygen. This effect, which is almost completely reversible by removing the oxygen, is attributed to the interaction of triplet P680 with triplet O2.

Benzyl Viologen↗
PubMed1991

Influence of clinical variables on triplet birth weight.

The small size of most reported triplet series has resulted in conflicting statements about the influence of several clinical variables on triplet birth weight. Therefore, obstetrical and neonatal data were collected on 196 mothers and their 580 infants (8 stillbirths excluded). Gestational age was based on the date of fertilization in 13 IVF triplets and on the date of ovulation in 90 medically induced triplets. Obstetrical and ultrasonic criteria were used to estimate the date of confinement in 93 spontaneous triplets. Birth weight appeared to be higher in males and with higher maternal parity, independent of gestational age. The apparent effect of medical technologies such as ovulation induction or IVF on combined triplet birth weight disappeared when maternal parity and fetal gender were controlled. Preeclampsia, maternal race and zygosity were not significantly associated with birth weight. While birth order did not significantly effect ultimate birth weight, the heaviest triplet did present first more often than would be expected by chance alone. Future evaluation of neonatal outcome data in multifetal gestations should control for gestational age, fetal gender and maternal parity. It appears that triplet birth weight is not affected by etiology, which is important given the significant impact of medical technologies.

Analysis of Variance↗
PubMed1992

[Triplets and quadruplets in Switzerland, 1985-1988].

To determine the incidence of multiple births and associated morbidity and mortality, we collected in a retrospective study all the multiple births (twins excluded) in Switzerland from 1985 to 1988. In all we followed 77 sets of triplets and 9 sets of quadruplets, representing an annual incidence of 1/3968 births for the triplets and 1/33,947 births for the quadruplets. The incidence of induced pregnancies increased in the period 1985 to 1988. The principal complications were premature contractions and preeclampsia. Only 56% of the children were born in a hospital with a neonatal intensive care unit. The mean gestational age was 33 0/7 weeks (ranging from 25 0/7 to 38 5/7) for the triplets, and 30 5/7 weeks (ranging from 27 5/7 to 36 3/7) for the quadruplets. The mean birthweight was 1787 g (ranging from 560 to 3000 g) for the triplets and 1189 g (ranging from 590 to 1980 g) for the quadruplets. RDS was found to be the principal neonatal pathology (65.5% of triplets and 85.2% of quadruplets) with 18.8% of triplets and 61.8% of quadruplets requiring ventilation. The mortality rate in our study was 8.9% for triplets and 14.7% for quadruplets.

Birth Weight↗
PubMed1991

[An analysis of cephalometric polygons in 21 sets of triplets].

Lateral cephalometric radiographs of 21 sets of triplets (4 monozygotic, 12 dizygotic and 5 three zygotic) were used for this study. The following two polygons were analysed: SNA and NSAr Go Me. Superimposition of the cephalometric tracings was made on the S-N line with S as the registration point. Intra- and inter-set comparisons between monozygotic (MZ), dizygotic (DZ) and three zygotic (TZ) triplets were made. Members of MZ triplets demonstrated the greatest similarity in size and form of the polygons. The second greatest similarity was found between MZ members of the DZ triplets, while the third DZ member of all such triplets showed much higher difference compared with the MZ members. Finally, triplets of TZ sets demonstrated the greatest difference between each other. The results obtained from this study indicated that genetic factors played a dominant role in growth and development of the craniofacial complex. However, difference found between members of MZ triplets suggested an importance of environmental factors in these processes as well.

Cephalometry↗
PubMed1991

Neurofilament protein triplet immunoreactivity in the dorsal root ganglia of the guinea-pig.

Immunoreactivity for the neurofilament protein triplet was investigated in neurons of the dorsal root ganglia of the guinea-pig by using a battery of antibodies. In unfixed tissue, nearly all neurons in these ganglia demonstrated some degree of neurofilament protein triplet immunoreactivity. Large neurons generally displayed intense immunoreactivity, whereas most small to medium-sized neurons showed faint to moderate immunoreactivity. Double-labelling immunofluorescence demonstrated that most antibodies to the individual subunits of the neurofilament protein triplet had the same distribution and intensity of labelling in sensory neurons. Increasing durations of tissue fixation in aldehyde solutions selectively diminished neurofilament protein triplet immunoreactivity in small to medium-sized neurons. Double-labelling with neurofilament protein triplet antibodies in combination with antibodies to other neuronal markers, such as neuron-specific enolase, substance P and tyrosine hydroxylase, showed that tissue processing conditions affect the degree of co-localization of immunoreactivity to the neurofilament protein triplet and to these other neuronal markers. These results indicate that, with a judicious manipulation of the duration of tissue fixation, neurofilament protein triplet immunoreactivity can be used in combination with other neuronal markers to distinguish groups of neurons according to their size and chemical coding.

Animals↗
PubMed1992

The neurofilament triplet is present in distinct subpopulations of neurons in the central nervous system of the guinea-pig.

It is commonly assumed that most, if not all, neurons contain the intermediate filament protein class known as the neurofilament protein-triplet. The following study investigated the distribution of neurofilament protein-triplet immunoreactivity in selected regions of the guinea-pig central nervous system using monoclonal antibodies directed against phosphorylation-independent epitopes on the three subunits under optimal tissue processing conditions. Neurofilament protein-triplet immunoreactivity was present in distinct subpopulations of neurons in the cerebellar cortex, neocortex, hippocampal formation, retina, striatum and medulla oblongata. In many of these regions, labelled neurons represented only a small proportion of the total. The selective distribution of this intermediate filament protein class was confirmed in double-labelling experiments using antibodies to the neurofilament protein-triplet in combination with antibodies to other neuronal markers. The distribution of neurofilament protein-triplet immunoreactivity also correlated with the distribution of staining observed with a silver impregnation method based on Bielschowsky. The present results in combination with previous observations have demonstrated that the neurofilament protein-triplet is found in specific subclasses of neurons in different regions of the nervous system. Content of this intermediate filament protein class does not appear to be correlated with neuronal size or length of projection. These results also suggest that the selectivity of staining between neuronal classes observed with classical silver impregnation methods may be due to the presence or absence of the neurofilament protein-triplet. The present results may also provide a new perspective on the basis of the selective vulnerability of neurons in degenerative diseases.

Animals↗
PubMedDate not supplied

Complementary immunohistochemical distribution of the neurofilament triplet and novel intermediate filament proteins in the autonomic and sensory nervous system of the guinea-pig.

We have previously established that immunoreactivity for the triplet of polypeptides that comprise the class IV intermediate filament proteins (NFP-triplet) is localized in specific subpopulations of neurons in guinea-pig sensory and autonomic ganglia. Antibodies to novel neurofilament proteins, including a polyclonal antibody to a 57 kDa neuronal intermediate filament polypeptide (NIF57kD) and a monoclonal antibody (CH1) to a 150 kDa intermediate filament, or associated, protein were used in combination with antibodies to the NFP-triplet for double-labelling immunohistochemistry. The results show that different subpopulations of neurons in the guinea-pig dorsal root ganglia, coeliac ganglion and enteric ganglia can be distinguished by their complementary immunoreactivity for these proteins. In dorsal root ganglia, larger neurons are intensely immunoreactive for the NFP-triplet while immunoreactivity with CH1 and NIF57kD antibodies is restricted to the small to medium-sized neurons. In the coeliac ganglion, two regionally defined subpopulations of neurons can be distinguished by their immunoreactivity for either the NFP-triplet or NIF57kD, whereas CH1 labels all neurons with equal intensity. Three classes of morphologically distinct myenteric neuron subpopulations are also distinguished by their immunoreactivity for either the NFP-triplet, NIF57kD or CH1 antibodies. Two classes of submucous neurons are labelled both with CH1 and NIF57kD antibodies but show faint or no immunoreactivity for the NFP-triplet. It is concluded that intermediate filament protein immunoreactivity marks different subpopulations of neurons, which suggests that these proteins may have specific roles in neuronal function.

Animals↗
PubMed1992

Structure of a G.T.A triplet in an intramolecular DNA triplex.

A 32-base DNA oligonucleotide has been studied by one- and two-dimensional 1H NMR spectroscopy and is shown to form a stable, pyr.pur.pyr, intramolecular triple helical structure, with a four C loop and a TATA loop connecting the Watson-Crick- and Hoogsteen-paired strands, respectively. This triplex contains five T.A.T base triplets, two C+.G.C base triplets, and an unusual G.T.A base triplet which disrupts the pyr.pur.pyr motif. The G.T.A triplet consists of a Watson-Crick T.A base pair, with the T situated in the "purine strand" and the A situated in the "pyrimidine strand" and a G situated in the Hoogsteen-base-paired "pyrimidine strand" hydrogen bonded to the T. The base-pairing structure of the G.T.A triplet has been investigated and has been found to involve a single hydrogen bond from the guanine amino group to the O4 carbonyl of the thymine, leaving the guanine imino proton free. The specific amino proton involved in the hydrogen bond is the H2(2) proton. This orients the guanine such that its sugar is near the thymine methyl group. The guanine sugar adopts an N-type (C3'-endo) sugar pucker in this triplet. The stability of the G.T.A triplet within pyr.pur.pyr triplexes is discussed.

Base Composition↗
PubMed1991

Differential changes in expression of the neurofilament triplet protein-immunoreactivity in Purkinje cells of the cerebellum during the postnatal development of rats.

By means of peroxidase-anti-peroxidase (PAP) immunohistochemistry with both the neurofilament (NF) triplet (small: 68 K, medium: 150 K, high: 200 K) antisera and the antiserum against spot 35-calbindin, developmental changes in expression of the immunoreactivity for the NF triplet proteins in different domains of the Purkinje cells was examined in the cerebella of postnatal rats. From birth till the postnatal day 6 (P6) the somata and dendrites exhibited moderately positive immunoreaction for small and medium NF subunits. In contrast, the incubation for the high NF subunit resulted in a negative immunoreaction for the somata and dendrites of the Purkinje cells at those stages. On P8 and P10 they were weakly immunoreactive for all NF triplet. Thereafter the intensity of their immunoreaction decreased progressively and the Purkinje cell somata and dendrites were immunonegative for all NF triplet proteins on P21, when the Purkinje cell attained an adult appearance in morphology. On the other hand, the Purkinje cell axons, which can be identified selectively by the positive immunoreaction for the spot 35-calbindin throughout the course of the postnatal development, exhibited positive immunoreactivity for all the NF triplet on the 9th, 21th and 50th postnatal days in the cerebellar white matter. The development of the slow axoplasmic transport and the posttranslational modification of the NF triplet proteins are discussed as possible mechanisms underlying the differential expression of the immunoreactivity for the NF triplet proteins in different domains of the Purkinje cells during postnatal development.

Animals↗
PubMedDate not supplied

[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↗