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At least 19 recordsLinked to original sources
PubMed1979

Discrimination of uniform spectrum pulse sequences.

Random polarity-modulated sequences were produced with a uniform short-term spectrum over defined sampling intervals by a method described by Pierce, Lipes, and Cheetham [J. Acoust. Soc. Am. 61, 1609-1621 (1977)]. These are identified as PLC sequences. By contrast, unconstrained random polarity-modulated pulse trains with a constant interpulse interval may depart from a short-term uniform spectrum. It is shown that listeners can clearly discriminate between PLC sequences and unconstrained random sequences, and can discriminate among different PLC sequences. This discrimination is more nearly related to the statistical redundancy of the PLC sequences. This discrimination is more nearly related to the statistical redundancy of the PLC sequences than to their run-length distribution. Such discrimination is relatively resistant to moderate degrees of temporal jitter and is obtained with other forms of information coding. Discrimination of PLC sequences is presumably based upon phase information.

Acoustic Stimulation↗
PubMed1977

Exciton annihilation in the two photosystems in chloroplasts at 100 degrees K.

The fluorescence yield (F) of spinach chloroplasts at 100 degrees K measured at 735 nm (photosystem I fluorescence-F 735) and at 685 nm (photosystem II fluorescence-F 685) has been determined with different modes of laser excitation. The modes of excitation included a single picosecond pulse, sequences of picosecond pulses (4, 22, and 300 pulses spaced 5 ns apart) and a single nonmode-locked 2-mus pulse (MP mode). The F 735/F 685 intensity ratios decrease from 1.62 to 0.61 when a single picosecond pulse (or low-power continuous helium-neon laser) is replaced by excitation with the 300-ps pulse train (PPT mode) or MP mode. In the PPT mode of excitation, the 735-nm fluorescence band is quenched by a factor of 45 as the intensity is increased from 10(15) to 10(18) photons/cm(2) per pulse train and the 685-nm fluorescence is quenched by a factor of 10. In the MP mode, the quenching factors are 25 and 7, respectively, in the same intensity range. Fluorescence quantum yield measurements with different picosecond pulse sequences indicate that relatively long-lived quenching species are operative, which survive from one picosecond pulse to another within the pulse train. The excitonic processes possible in the photosynthetic units are discussed in detail. The differences in the quenching factors between the MP and PPT modes of excitation are attributed to singlet-singlet annihilation, possible when picosecond pulses are utilized, but minimized in the MP mode of excitation. The long-lived quenchers are identified as triplets and/or bulk chlorophyll ions formed by singlet-singlet annihilation. The preferential quenching in photosystem I is attributed to triplet excitons. The influence of heating effects, photochemistry, bleaching, and two-photon processes is also considered and is shown to be negligible.

Chloroplasts↗
PubMed1977

Spin-lattice relaxation times for 13C in isotope-enriched glycine accumulated in frog muscle.

Spin-lattice relaxation times (T1's) of 13C-enriched glycine accumulated in frog muscles were determined at 1 degrees C by the inversion-recovery (180 degrees -tau-90 degree pulse sequence) method and compared with the values obtained in free solution. The value of T1 for the alpha-13C nucleus of glycine in the tissue was 50% of that obtained in free solution. The observed value for T1 in the tissue was not concentration-dependent, and no difference in chemical shift was observed between tissue and free solution. Quantification of the area under the glycine peak suggested that the observed signal represents at least 80% of the intracellular glycine. An average nuclear Overhauser enhancement of 2.83 for intracellular glycine indicates that the relaxation mechanism within the cell is predominantly dipolar, as in free solution. The value of T1 for the 13C' nucleus of glycine in the tissue was 67% of that in a solution of similar concentration. A quantitative analysis of the findings suggests that the observed difference in the value of T1 between tissue and free solution results from a difference in viscosity. The data provide no evidence either for special organization of intracellular water or for glycine binding. It is proposed that intracellular diffusion coefficients may be determined from measurements of 13C T1's of 13C-enriched intracellular solutes.

Animals↗
PubMed1978

Study of the tryptophan residues of lysozyme using 1H nuclear magnetic resonance.

The identification and complete assignment of the C-2 and N-1 proton nuclear magnetic resonances (NMR) of the six tryptophan residues of hen lysozyme are reported. Identification of the resonances required a detailed examination of the spectra of the protein in H2O and in 2H2O, and involved the application of spin-echo and Carr-Purcell-Meiboom-Gill pulse sequences. Assignment was achieved by observing the effects on the NMR spectra of performing specific chemical modifications, of binding paramagnetic species (lanthanide ions and spin labels), of binding inhibitors and protons and of carrying out solvent exchange experiments. The problems involved in completion of assignment are fully discussed. In the course of performing experiments to make assignments, several interesting aspects of the behaviour of the tryptophan residues in the protein structure were observed and are discussed.

Acetylglucosamine↗
PubMed1978

Reactivation of membrane charge movement and delayed potassium conductance in skeletal muscle fibres.

1. Intramembrane charge movement has been measured in striated muscle subjected to prolonged depolarization but repolarized to -100 mV for up to 100 sec. The method of measurement allows identification of charge or charges which are 'reprimed' by repolarization. 2. Charge 'reprimed' by repolarization appears to differ in its voltage distribution from charge detected in a permanently polarized fibre. The difference is probably due to the different pulse sequences used in the two measurements and to the fact that there appear to be several species of intramembrane charges with different transition potentials and different steepness of voltage distribution (V and k in eqn. (14): see below). 3. Potassium conductance is reprimed by repolarization following inactivation by depolarization. When the repriming potential is -100 mV the process appears to be in two stages; repriming to a value rather less than half the final value takes place exponentially with a time constant of approximately 40 sec; subsequently repriming to the final value is very slow. At a repriming potential of -140 mV repriming to the final value )1--2 mmho/microF) takes place exponentially with a time constant of approximately 17 sec.

Animals↗
PubMedDate not supplied

A feasibility study of prompt capture gamma in vivo neutron activation analysis.

The feasibility of using the information contained in the radiative capture gamma ray spectrum of the neutron-irradiated human body to measure quantitatively total body elemental composition in vivo has been investigated. Results of time dependent Monte Carlo simulations have shown that spectral interference of nonradiative capture origin can be completely eliminated by pulsing the detector/spectrometer system in anticoincidence with the neutron source. Calculations based on the results of the Monte Carlo simulation and on an experimental measurement of the efficiency versus energy characteristics of a Ge(Li) detector suggest that the primary limitation of the proposed technique would be inter-element spectral interference rather than inadequate detector sensitivity. Experimental measurements using a pulsed 14-MeV neutron generator and Ge(Li) gamma-ray spectrometer have produced results that are consistent with the predictions of the theoretical model. A radiative capture gamma-ray spectrum of a tissue-equivalent phantom was measured in pulsed mode and analyzed offline using a computerized spectral analysis procedure. The results were scaled to a proposed facility consisting of a 2.5-MeV pulsed neutron source and a detection system comprising two 50-cm3 (Ge(Li) detectros past which the subject would be scanned. It has been shown that in principle the elements hydrogen, chlorine, calcium, and nitrogen [the latter using large NaI(T1) detectors] could be measured with such a facility at an average body dose level of 0.1 rad. At this dose level the coefficients of variation based on counting statistics alone would be +/- 2%, or better, for these four elements. With an improvement in the detector/spectrometer energy resolution, the elements sulfur and carbon might also be measurable. It is also shown that by modifying the pulsing sequence appropriately and using 14-MeV neutrons, total body oxygen could also be measured at the 0.1 rad dose level via its inelastic neutron scattering deexcitation gamma activity.

Activation Analysis↗
PubMed1977

NMR in cancer: VIII. Phosphorus-31 as a nuclear probe for malignant tumors.

Spin-lattice relaxation times (T1) for 31P were determined in normal and malignant tissues by a saturation technique employing a 90 degree -tau-90 degrees pulse sequence. Results for five normal tissues from rat were (in seconds): 2.33 +/- .14 for liver; 2.19 +/- .05 for muscle; 1.13 +/- .05 for brain; 1.43 +/- .15 fro kidney; and 1.97 +/- .12 for intestine. Results for two rat malignancies, Novikoff hepatoma and Walker sarcoma, were 5.98 +/- .57 and 5.38 +/- .68, respectively, and for Crocker sarcoma of mouse, 5.19 +/- 1.42. No individual measurement of malignant tissue overlapped any of the normal measurements; probabilities of insignificance ranged from .029 for Crocker sarcoma to .000184 for Novikoff hepatoma. The data call attention to another nucleus of potential value for NMR detection of internal malignancies in humans. Also suggested, because of the strategic placement of the 31P nucleus in the nucleic acid molecule, is a possible new probe for exploring the mechanism of carcinogenesis.

Animals↗
PubMed1976

Molecular aspects of electrical excitation in lipid bilayers and cell membranes.

Several compounds of fungal or bacterial origin (EIM, alamethicin, monazomycin, DJ400B) can be incorporated into planar lipid bilayers where they form molecular channels and generate voltage-dependent ion conductances. When studied by voltage clamp, the kinetic and steady-state characteristics of these conductance changes are in every respect identical to those found in excitable cell membranes, and their major aspects can be quantitatively described by the Hodgkin-Huxley equations. Thus, the steady-state conductance is an expotential function of the membrane potential, the conductance rises with a sigmoid time course and decays exponentially, and the time constants of the conductance changes go through a maximum as a function of the potential. The conductances also show inactivation as seen in the sodium channels of nerve and the potassium channels of muscle. In addition, there appear for particular pulsing sequences certain kinetic transients that cannot be accounted for by the Hodgkin-Huxley equations but are also seen in identical form in nerve. Because the kinetics are identical in all excitable cell membranes and in these bilayers, it is likely that, in spite of the diverse chemical nature of the channel-forming molecules in the bilayers and the widely differing ion selectivities in the cellular systems, the mechanism by which the membrane opens and closes for the flow of ions is essentially the same in all cases. The kinetic data imply that a cooperative process is involved in the gating action. In principle, two different concepts could account for the kinetics--one involving an intramolecular configurational change within a complex permanent channel, the other, the assembly of a channel through the voltage-dependent aggregation of monomeric channel precursors. In the bilayers the high-order dependence of the steady-state conductance and of the gating time constants on the concentration of the channel formers suggests an aggregation mechanism in which the gating involves the voltage-induced insertion of all or part of the channel-forming molecules from the membrane surface into the hydrocarbon region and their subsequent aggregation into open channels by lateral diffusion. The mathematical description of this two-step insertion-aggregation mechanism accounts quantitatively for the entire conductancb-voltage kinetics including inactivation and other kinetic features which deviate from the Hodgkin-Huxley kinetics in the sense that the rate constants of the changes are dependent not only on the membrane potential but also on the value of the conductance and on time. The proposed mechanism is also in agreement with single-channel data for alamethicin which suggest that both the insertion and the aggregation rate constants are voltage-dependent...

Alamethicin↗
PubMed1979

Analysis of the message-sequence content of the pulse-labeled poly(A)+ heterogeneous nuclear RNA from HeLa cells by cDNA-excess hybridizations.

The message-sequence content of pulse-labeled poly(A)+ HeLa heterogenous nuclear RNA (hnRNA) has been examined by hybridizations to an excess of message cDNA. Control experiments show that the message cDNA accurately reflects the sequence distribution of the complex mixture of poly(A)+ messages present in the HeLa cytoplasm. Pulse-labeled poly(A)+ molecules in both the lamina-associated and shnRNA fractions contain message sequences, and approximately 65% of the poly(A)-adjacent hnRNA sequences are homologous to the 3' ends of mRNA. The majority of the pulse-labeled hnRNA molecules contain abundant message sequences. By use of these techniques it is also shown that some pulse-labeled polyadenylated message sequences are still synthesized in the presence of the adenosine analogue 5,6-dichloro-beta-D-ribofuranosylbenzimidazole under conditions where little or no new cytoplasmic mRNA is produced.

Base Sequence↗
PubMed1979

Signal detection in computer-synthesized noise.

Human observers detected sinusoidal and pulse-train signals in noise derived from two computer-synthesized sources and from a Gaussian noise source. The synthesized noise stimuli were generated from sequences of pulses whose amplitudes were drawn from two divergent types of probability distributions: a centrally peaked distribution and a bimodal distribution. No differences in the detectability of signals in these noise stimuli were evident at pulse rates of 1000, 2000, 4000, or 10 000 Hz. subjects could not discriminate between the two types of computer-generated maskers at any pulse rate. The data support a spectrum-analyzer model of detection in which multiband filtering of the input smooths the masker energy in each spectral region to approximate the Gaussian case.

Computers↗
PubMed2024

Advances in solid-state NMR methods for studying RNA structures and dynamics.

Ribonucleic acid (RNA) structures and dynamics play a crucial role in elucidating RNA functions and facilitating the design of drugs targeting RNA and RNA-protein complexes. However, obtaining RNA structures using conventional biophysical techniques, such as X-ray crystallography and solution nuclear magnetic resonance (NMR), presents challenges due to the inherent flexibility and susceptibility to degradation of RNA. In recent years, solid-state NMR (SSNMR) has rapidly emerged as a promising alternative technique for characterizing RNA structure and dynamics. SSNMR has several distinct advantages, including flexibility in sample states, the ability to capture dynamic features of RNA in solid form, and suitability to character RNAs in various sizes. Recent decade witnessed the growth of 1H-detected SSNMR methods on RNA, which targeted elucidating RNA topology and base pair dynamics in solid state. They have been applied to determine the topology of RNA segment in human immunodeficiency virus (HIV) genome and the base pair dynamics of riboswitch RNA. These advancements have expanded the utility of SSNMR techniques within the RNA research field. This review provides a comprehensive discussion of recent progress in 1H-detected SSNMR investigations into RNA structure and dynamics. We focus on the established 1H-detected SSNMR methods, sample preparation protocols, and the implementation of rapid data acquisition approaches.

Dynamics↗
PubMed1976

Actions of aldosterone on polyadenylated ribonucleic acid and Na+ transport in the toad bladder.

Polyadenylated ribonucleic acid [poly(A)(+)-RNA] has been isolated from the cytoplasm of the epithelium of the urinary bladder of the toad (Bufo marinus) by oligo-(deoxythymidylate)cellulose chromatography. Aldosterone increased the incorporation of [3H]uridine, and of [3H]uridine and [3H]adenosine (given in combination) into 7S, 12S, and 18S poly(A)(+)-RNA during the first 30 min of the action of the hormone, as defined by either a pulse or pulse-chase sequence. The quantity of cytoplasmic poly(A)(+)-RNA that hybridized to [3H]poly(uridine) was also increased by aldosterone. These results are consistent with the inference of induction of messenger RNA synthesis. This effect was most marked during the first 30 min of the action of the hormone.

Aldosterone↗
PubMed1977

Biosynthesis of ferritin in rat hepatoma cells and rat livers. I. Synthesis and assembly of protein subunits of ferritin.

Cell fractions were prepared from ACI rat livers and from rat hepatoma cell clone M-5123-C1. Radioimmunoassays of ferritin and of its protein subunits in various cell fractions after biosynthetic labeling with [14C]leucine were done by means of ferritin-specific and subunit-specific rabbit antibody. In both ACI rat livers and M-5123-C1 hepatoma cells free polyribosomes synthesized approximately 81% of the protein subunits of ferritin, and membrane-bound polyribosomes synthesized the rest. In both polyribosomal fractions, [14C]leucine-labeled subunits were detected earlier than [14C]leucine-labeled ferritin and apoferritin (5 min as against 30 min after initiation of a pulse). Time sequence studies of the shifts of biosynthetically labeled subunits and ferritin through different cell compartments provided evidence for vectorial transport of subunits and of ferritin, the direction of transport being from the two polyribosomal systems to the smooth membrane compartment and to the cytosol.

Animals↗
PubMed1976

Stability of "spacer" sequences of pre-ribosomal RNA in Escherichia coli.

"SPACER" SEQUENCES OF AN RRNA gene transcript were detected with high efficiency by hybridization with DNA of the specilized transducing phase phi80rrn. Hybridization-competition studies revealed that 20 to 23% of the 30S precursor rRNA, obtained from E. coli mutant strain AB301/105, consist of "spacer" sequences. The "spacer" sequences formed hybrids with E. coli DNA, but not with Vibrio DNA. Experiments with RNA labeling in the presence of rifampicin showed that more than 80% of the spacer sequences arrive in full-length 30S pre rRNA chains before any cleavage of the RNA occurs. The hybridization assays also permitted the detection of "spacer" sequences in pulse-labeled rRNA of wild-type cells, in which the 30S pre-rRNA is already cleaved during its synthesis. Many of these "spacer" sequences degraded to alcohol-soluble materials with a half-life time of 1.2 min. The half-life was not lengthened by the treatment of cells with chloramphenicol, which stabilizes bulk mRNA. However, unstable "spacer" sequences transcribed in cells deficient in RNase III exhibited slower degradation, with a half-life time of about 9 min, whereas the cleavage of 30S pre-rRNA to smaller RNA species occurred with a half-life of about 3 min. These results are consistent with the notion that a rate-limiting action of RNase III in the initial attack leads to degradation of "spacer" sequences in rRNA gene transcript; and that degradation is not at all connected with ribosome translocation.

Base Sequence↗
PubMed1976

The size of pulse-labeled fibroin messenger RNA.

A method has been developed for the isolation of fibroin gene transcripts from total RNA of the silkworm Bombyx mori. It is based on affinity chromatography using Sephadex-bound polynucleotides capable of selectively hybridizing with fibroin mRNA sequences. In vivo pulse labeling of the posterior silk gland for periods of 10-35 min produces labeled heterogeneous nuclear RNA of high molecular weight (greater 40S). Fibroin gene transcripts can be selected from the total hnRNA population by two consecutive passages through the affinity column. Analysis of the column-bound material in denaturing polyacrylamide-agarose gels reveals that the size of pulse-labeled fibroin mRNA is essentially the same (within 5%) as that of mature cytoplasmic mRNA. This holds true for pulses as short as 6 min, where even nascent mRNA can be observed. However, a small shoulder of material is present on the heavy side of the pulse-labeled mRNA, which could be indicative of an extremely short-lived precurosr species. The purified pulse-labeled mRNA (10 min incorporation) has been further analyzed by chromatography in oligo(dT)-cellulose. The data show that the mRNA is polyadenylated within a few minutes after synthesis.

Animals↗
PubMed1978

Precordial mechanical stimulation for exposing electrical instability in the ischemic heart.

Sequenital mechanical pulsing of the chest wall with three stimuli failed to induce arrhythmias in normal dogs. After coronary arterial occlusion, this technique evoked in 11 of 12 animals repetitive ventricular tachycardia in 2. These responses corresponded closely to those elicited by electrical testing. In four conscious animals after recovery from myocardial infarction, precordial pulsing induced repetitive ventricular arrhythmias. The type of arrhythmia produced depended on the degree of prematurity of the third pulse in the sequence. The use of precordial mechanical stimulation can perhaps be modified and adapted as a method of detecting persons at high risk for sudden cardiac death.

Animals↗
PubMed1978

Transient potassium currents in slow muscle fibers.

Transient changes in potassium conductance in chronically depolarized slow muscle fibers have been studied using a voltage clamp method. The transient behavior included current decays from initial to steady state for hyperpolarizing and depolarizing voltage clamp steps. A two-pulse voltage clamp sequence (conditioning step followed by test step) showed the initial potassium test current to depend sigmoidally on conditioning potential implicating the involvement of a membrane-bound charged group in regulating potassium current.

Animals↗
PubMed1979

Processing of common precursor forms of adrenocorticotropin and endorphins in cultures of mouse pituitary cells and in mouse pituitary.

The initial steps in the processing of the common precursor to adrenocorticotropin (ACTH) and beta-lipotropin (beta-LPH) in mouse pituitary cells (AtT-20) have been investigated. Three forms of the precursor have been resolved by sodium dodecyl sulfate (NaDodSO4) polyacrylamide gel electrophoresis with apparent molecular weights of 29,000, 32,000 and 34,000 (29K, 32K, and 34K ACTH-endorphin). The three precursor forms have a very similar peptide backbone, but their carbohydrate content differs. In particular, a tryptic glycopeptide has been observed in 32K ACTH-endorphin which is not present in 29K ACTH-endorphin and has been identified as a tryptic peptide containing the alpha(22--39) sequence of ACTH. Pulse chase and continuous-labeling studies with radioactive amino acids and sugars suggest that the 29K form is converted to the 32K and 34K forms of the precursor by the addition of carbohydrate. The glycopeptide and pulse chase studies suggest that 29K ACTH-endorphin can either be converted to 4.5K ACTH by proteolytic processing or to 32K ACTH-endorphin by the further addition of carbohydrate.

Adrenocorticotropic Hormone↗