Effects of erythromycin on membrane-bound chloroplast ribosomes from wild-type Chlamydomonas reinhardi and erythromycin-resistant mutants

The properties of peripheral cutaneous units in the hairy skin of cat's forelimb were studied by single-fiber recordings with tungsten microelectrodes. The response properties and receptive field (RFs) of total 193 units in superficial branch of radial nerve (SRN) were studied. The SRN sample included the following five major types of mechanoreceptive units; two types of low-threshold units (type I and II, slowly adapting), two types of hair units (G and D, rapidly adapting) and field units (F, responding principally to slow skin movement). Afferent conduction velocities of these units ranged from 9.0 to 56.0 m/sec. D hair fibers conducted much slower than other types of afferents and their conduction velocities were between 9.0 and 23.3 m/sec. Most of the smaller RFs of G, D and F units were found in the paw and digits. The disto-proximal increase of the mean size of RFs was marked in D hair units. The distributions of the RFs of simultaneously recorded paired units, which were supposed to be adjacent fibers, were examined. Among 23 paired units, more than half of them were homonymous combinations of unit types and there were no marked prevalence of particular types in heteronymous combinations. The RFs of paired units were close to each other, but showed little overlaps and some were separated by up to several cm over the skin surface. Some functional properties of cutaneous afferents from the forelimb were discussed.     

Spectral properties and energy transfer of Tm3+/Ho3+-codoped Ca2O3-Bi2O3-GeO2-PbO glasse

The 2.0 μm emission originating from Ho3+:5I7→5I8 transition in Ho3+/Tm3+-codoped gallate-bismuth-germanium-lead glasses →5I8 transition in Ho3+/Tm3+-codoped gallate-bismuth-germanium-lead glasses were investigated upon excitation with 808 nm laser diode (LD). Energy transfer (ET) process between Tm3+: 3I4 level and Ho3+: 5I7 level nergy transfer (ET) process between Tm3+: 3I4 level and Ho3+: 5I7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho3+-doped bis-It was noted that the measured peak wavelength and stimulated emission cross-section of Ho3+-doped bis-muth-germanium-lead glasses were ～2.02 μm and 5.1×10-21 cm2, respectively. Intense emission of Ho3+ in Tm3+/Ho3+-codoped GBPG glass ×10-21 cm2, respectively. Intense emission of Ho3+ in Tm3+/Ho3+-codoped GBPG glass were observed, which resulted from the ET between Tm3+: 3I4 and Ho3+: 5I7 level upon excitation with 808 nm LD. the ET between Tm3+: 3I4 and Ho3+: 5I7 level upon excitation with 808 nm LD.     

Spectral properties and energy transfer of Tm~(3 )/Ho~(3 )-codoped Ga_2O_3-Bi_2O_3-GeO_2-PbO glasses

The 2.0 μm emission originating from Ho3 :5I7→5I8 transition in Ho3 /Tm3 -codoped gallate-bismuth-germanium-lead glasses were investigated upon excitation with 808 nm laser diode (LD). Energy transfer (ET) process between Tm3 : 3F4 level and Ho3 : 5I7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho3 -doped bis-muth-germanium-lead glasses were ～2.02 μm and 5.1×10–21 cm2, respectively. Intense emission of Ho3 in Tm3 /Ho3 -codoped GBPG glass were observed, which resulted from the ET between Tm3 : 3F4 and Ho3 : 5I7 level upon excitation with 808 nm LD.     

Benzene ring impact on energy transfer system of Eu(TTA)3DPBT

Eu(TTA)₃DPBT was found most likely to lead a special singlet photosensitization pathway by means of time-resolved luminescence spectroscopic studies. For further understanding of its intra-molecular energy transfer mechanism, another lanthanide complex Eu(TTA)₃BDDT was synthesized, using a related ligand BDDT, changing the D-p-A structure of DPBT to the D-A structure of BDDT. The luminescence characteristics of both complexes were investigated and compared. Results show that p bridge plays an important role in the energy transfer process. p bridge can change the charge separation strength by affecting the electron-density distribution over the diethylaniline and the dipyrazoletriazine moieties. Without the p bridge connection, the benzene ring, BDDT gets a smaller conjugated system, and the absorption peak in the UV-Vis spectrum of BDDT has a blue shift of 114 nm relative to that of DPBT. So the energy level of ligand BDDT and the central ion Eu(III) does not match well, and the energy transfer efficiency drop 33%.     

Spectral properties and energy transfer of Tm^3＋/Ho^3＋-codoped Ga2O3-Bi2O3-GeO2-PbO glasses

The 2.0 μm emission originating from Ho^3＋：^5I7→^5I8 were investigated upon excitation with 808 nm laser diode （LD） transition in Ho^3＋/Tm^3＋-codoped gallate-bismuth-germanium-lead glasses Energy transfer （ET） process between Tm^3＋： ^3F4 level and Ho^3＋： ^5I7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho^3＋-doped bismuth-germanium-lead glasses were -2.02 μm and 5.1×10^-21 cm^2, respectively. Intense emission of Ho^3＋ in Tm^3＋/Ho^3＋-codoped GBPG glass were observed, which resulted from the ET between Tm^3＋： ^3F4 and Ho^3＋： ^5I7 level upon excitation with 808 nm LD.     

Structural studies of the melibiose permease of Escherichia coli by fluorescence resonance energy transfer. II. Identification of the tryptophan residues acting as energy donors

In the accompanying paper, we demonstrated the presence of a fluorescence resonance energy transfer (FRET) between the tryptophans of the melibiose permease (MelB) of Escherichia coli and a fluorescent sugar, 2'-(N-5-dimethylaminonaphthalene-1-sulfonyl)aminoethyl-1-thio-beta-D- galactopyranoside (Dns2-S-Gal) bound at the sugar-binding site (Maehrel, C., Cordat, E., Mus-Veteau, I., and Leblanc, G. (1998) J. Biol. Chem. 273, 33192-33197). To identify the tryptophans that transfer their energy to the fluorescent sugar, we analyzed the FRET properties of MelB mutants carrying the replacement of each of the eight MelB tryptophans by a phenylalanine. The data indicate that Trp64, localized in loop 2-3 from the N-terminal domain, and Trp299, localized in helix IX in the C-terminal domain, are responsible for up to 80% of the FRET signal. Moreover, by assuming that only Trp299 transfers energy to Dns2-S-Gal in mutant W64F, whereas only Trp64 transfers energy to Dns2-S-Gal in mutant W299F, we calculated that Trp299 and Trp64 are about 14 and 20 A away from the probe, respectively. In addition, we observed that mutating Trp342, localized in helix X of the C-terminal domain, produces a significant increase of the polarity of the fluorescent sugar environment, suggesting its proximity to the sugar-binding site. Taken together, these data provide additional support for the suggestion that (i) the sugar-binding site is localized in the C-terminal part of the transporter, probably close to membrane segments IX and X, and (ii) the N-terminal domain, and particularly cytoplasmic loop 2-3, is also close to the sugar-binding site.     

Luminescence properties of BaAl12O19:Tb,Ce and energy transfer between Ce3+, Tb3+

BaAl₁₂O₁₉:Tb,Ce phosphors were prepared by sol-gel technique, the crystalline structures of samples characterized by XRD, and the luminescence properties and energy transfer between Ce³⁺ and Tb³⁺ were investigated. The results indicated that the emission intensity and the excitation wavelength range of Tb³⁺ increased when Ce³⁺ was doped. It demonstrated that the Ce³⁺ added in the BaAl₁₂O₁₉:Tb could deliver energy to Tb³⁺, and Ce³⁺ was not luminous by itself. The relative emission intensity of Tb³⁺ at wavelength of 548 nm was the strongest by Tb³⁺/Ce³⁺ ratio of 2:1, when excited at 310 nm, which was the characteristic adsorption wavelength of Ce³⁺.     

Photoluminescence properties and energy transfer of a single-phased white-emitting NaAlSiO_4:Ce~(3+),Sm~(3+) phosphor

A series of tunable phosphors NaAlSiO_4:Ce~(3+),Sm~(3+) were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation(325 nm), NaAlSiO_4:Ce~(3+),Sm~(3+) showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce~(3+) and ~4G_(5/2)→~6H_J(J=5/2, 7/2, 9/2, 11/2) transition of Sm~(3+), respectively. In addition, we studied the detailed energy transfer process between Ce~(3+) and Sm~(3+) and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce~(3+), Sm~(3+) co-doped phosphors with the color coordinate(x=0.313, y=0.283) could be observed under 325 nm excitation, which was close to the ideal white light(x=0.33, y=0.33). The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes(UV-WLEDs).     

Studies on the lithium transport across the red cell membrane. I. Li+ uphill transport by the Na+-dependent Li+ counter-transport system of human erythrocytes

Li+ net-transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1-2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+. The following results were obtained: 1. Li+ is extruded from glycolyzing erythrocytes against an electrochemical gradient until a steady-state Li+ distribution is established after 24-28 h. 2. The initial rate of Li+ extrusion is not altered by ouabain or by reduction of ATP levels to less than 25% of the normal value. 3. Replacement of external Na+ by K+ or choline+ abolishes the establishment of an electrochemical Li+ gradient. 4. The Li+ distribution ratio Lie+/Lii+ increases proportional to the ratio Nae+/Nai+ at constant extravellular K+ concentrations. 5. In ghost suspension an uphill Li+ transport is driven by an oppositely directed Na+ gradient. The direction of the Li+ uphill transport can be reversed by reversing the Na+ gradient. From the results it is concluded that the Li+ uphill transport across human red cell membranes is mediated by a Na+-dependent Li+ counter-transport system. This system is not inhibited by ouabain and does not appear to be identical to the Na+-Na+ exchange system described by Garrahan and Glynn.     

Kinetic analysis of pairing and strand exchange catalyzed by RecA. Detection by fluorescence energy transfer

RecA is a 38-kDa protein from Escherichia coli that polymerizes on single-stranded DNA, forming a nucleoprotein filament that pairs with homologous duplex DNA and carries out strand exchange in vitro. In this study, we measured RecA-catalyzed pairing and strand exchange in solution by energy transfer between fluorescent dyes on the ends of deoxyribo-oligonucleotides. By varying the position of the dyes in separate assays, we were able to detect the pairing of single-stranded RecA filament with duplex DNA as an increase in energy transfer, and strand displacement as a decrease in energy transfer. With these assays, the kinetics of pairing and strand displacement were studied by stopped-flow spectrofluorometry. The data revealed a rapid, second order, reversible pairing step that was followed by a slower, reversible, first order strand exchange step. These data indicate that an initial unstable intermediate exists which can readily return to reactants, and that a further, rate-limiting step (or steps) is required to effect or complete strand exchange.     

Spectral variations of Ca3Sc2Si3O12:Ce phosphors via substitution and energy transfer

The luminescence intensity of emission peak at around 525 nm decreased in the Ce3+ and Er3+ co-doped Ca3Sc2Si3O12 phosphors. Mg2+ ion, which was likely incorporated into the Sc3+ position of the host crystal, was co-doped to adjust the crystal field and compensate for the excess positive charge due to the doping of Ce3+. The green emission belonged to the 5d→4f transition of Ce3+ moved toward longer wavelength by addition of Mg2+ in Ce3+ and Er3+ co-doped Ca3Sc2Si3O12 phosphor, which could increase the brightness of the phosphor. However, the position of weakening of luminescence intensity at around 525 nm remained basically unchanged by increasing the amount of Mg2+. The results showed that the weakening of luminescence intensity at around 525 nm caused by the absorption of Er3+, which had little influence on the environment of the crystal field.     

Diffusion in the titanium-nickel system: I. occurrence and growth of the various intermetallic compounds

Various types of diffusion couples have been prepared and the growth of the layers, formed in these couples, has been studied in the temperature range between 550 and 940°C. All phases which, on the basis of the equilibrium diagram, could be expected under the circumstances, were found in the diffusion zone. The layer growth of β-Ti(Ni), Ti₂Ni and TiNi in all types of couples obeyed the parabolic law; the TiNi layer was the only exception. It is supposed that in this case grain boundary diffusion is responsible for the observed abnormal growth. The shape of the β-Ti/β-Ti + Ti₂Ni boundary in the equilibrium diagram was constructed using data, both from recorded penetration curves and from equilibrated two-phase alloys. Excellent agreement between the results of these two methods was obtained. The eutectoid composition at 77Q°C has been placed at about 7 at. pct Ni, in contrast with earlier results. Furthermore, the composition range of TiNi has been determined from penetration curves. This paper is based on a Thesis submitted by G. F. BASTIN in fulfillment or requirements for the degree of Doctor in Technological Sciences.     

Comparison of human and hamster mitochondrial transfer RNA. Physical properties and methylation status

In a comparative study, the effective of intraventricularly or intraperitoneally injected p-chloroamphetamine (p-CA) and some chloroindoles on cerebral levels of serotonin was evaluated. 5-Chloroindole depressed 5-HT levels in the brainstem and telencephalon for three days, 6-chloro-2-methylindole (6-CMI) only during the first day. 5-Chloroindazole had no effect at all. p-CA was more toxic to guinea pigs than to rats. p-CA and 5-chloro-2-methylindole (5-CMI) had no effect on cerebral 5-HT in chicks. Apparently, none of these compounds represented or was converted to a metabolite possibly responsible for the neurotoxic effects of p-CA.