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A Lapidot

Publications and source records attributed to A Lapidot.

At least 19 recordsLinked to original sources
PubMed1991

Formation of DNA triplexes accounts for arrests of DNA synthesis at d(TC)n and d(GA)n tracts.

To study the mechanism of arrest of DNA synthesis at d(TC)n and d(GA)n sequences, single-stranded DNA molecules including d(TC)27 or d(TC)31 tracts or a d(GA)27 tract were used as templates for in vitro assays of complementary DNA synthesis performed by extension of a primer with the Klenow polymerase or the Taq polymerase (Thermus aquaticus DNA polymerase). Electrophoresis of the products revealed that arrests occurred around the middle of these tracts. The arrests in the d(TC)n sequences were eliminated when dATP or dGTP was replaced with the analogue 7-deaza dATP or 7-deaza dGTP, respectively, or when the templates were preincubated with the Escherichia coli single-strand binding protein (SSB). Preincubation of the template including a d(GA)27 tract with SSB has also eliminated the arrests at this sequence. Furthermore, arrests did not occur at d[G(7-deaza A)]27 or d[(7-deaza G)A]27 tracts when molecules including such tracts were used as templates. These results are compatible with the notion that the arrests were caused by formation of d(TC)i.d(GA)i.d(TC)i and d(GA)i.d(GA)i.d(TC)i triplexes, in which the bases in the uncopied portions of the d(TC)n tracts, or of the d(GA)27 tract, and the purine bases in the newly synthesized d(TC)i.d(GA)i duplexes were bound by hydrogen bonds. In the assays performed with the Taq polymerase, the pH dependence (in the range of 6.0-9.0) and the temperature dependence of the arrests were determined. As the pH was lowered, the arrests in the d(TC)27 tract were enhanced, in line with the expected properties of d(TC)i.d(GA)i.d(TC)i triplexes. The arrests in the d(GA)27 tract were enhanced by an increase in the pH. At pH 7.2 the arrests in the d(GA)27 tract persisted up to 80 degrees C, whereas the arrests in the d(TC)27 tract were eliminated at 50 degrees C; these results presumably reflect the relative stabilities of the two triplexes mentioned above at this physiological pH value and could be biologically significant.

Adenine↗
PubMed1991

13C nuclear magnetic resonance and gas chromatography-mass spectrometry studies of carbon metabolism in the actinomycin D producer Streptomyces parvulus by use of 13C-labeled precursors.

Fructose and glutamate metabolism was monitored in cell suspensions of streptomyces parvulus by 13C nuclear magnetic resonance. The experiments were performed for cells grown with various 13C sources in a growth medium containing D-[U-13C]fructose, L-[13C]glutamate, or L-[U-13C]aspartate and with nonlabeled precursors to compare intracellular pools in S. parvulus cells at different periods of the cell life cycle. The transport of fructose into the cells was biphasic in nature; during rapid transport, mannitol, fructose, and glucose 6-phosphate were accumulated intracellularly, whereas during the passive diffusion of fructose, the intracellular carbohydrate pool comprised mainly trehalose (1,1'-alpha-alpha-D-glucose). The regulation of fructokinase activity by the intracellular intermediates may play an important role in fructose catabolism in S. parvulus. Transaldolase activity in S. parvulus was determined from the 13C nuclear magnetic resonance labeling pattern of trehalose carbons obtained from cells grown in medium containing either L-[U-13C]aspartate or L-[U-13C]glutamate. Only carbons 4, 5, and 6 of the disaccharide were labeled. Isotopomer analysis of the trehalose carbons led us to conclude that the flux through the reverse glycolytic pathway, condensation of glyceraldehyde 3-phosphate with dihydroxyacetone phosphate, makes at best a minor contribution to the 13C-labeled glucose units observed in trehalose. The pentose pathway and transaldolase activity can explain the labeling pattern of 4,5,6-13C3 of trehalose. Moreover, the transfer of the 13C label of L-[U-13C]aspartate into the different isotopomers of trehalose C4, C5, and C6 by the transaldolase activity allowed us to calculate the relative fluxes from oxaloacetate via gluconeogenesis and through the tricarboxylic acid cycle. The ratio of the two fluxes is approximately 1. However, the main carbon source for trehalose synthesis in S. parvulus is fructose and not glutamate or aspartate. The 13C enrichment and isotopomer population, measured by nuclear magnetic resonance and gas chromatography-mass spectrometry, of the actinomycin D peptide ring enabled us to specify the origins of the five amino acids of actinomycin D. Threonine and proline exhibited isotopomer populations similar to that of the extracellular L-[13C]glutamate, indicating that protein catabolism is the origin of their 13C label, whereas the isotopomer populations of sarcosine and N-methylvaline were similar to those of the new intracellular pool of S. parvulus that originated from D-[U-13C]fructose during the production of actinomycin D.

Carbohydrate Sequence↗
PubMed1979

Comparative in vivo nitrogen-15 nuclear magnetic resonance study of the cell wall components of five Gram-positive bacteria.

The proton-decoupled 9.12 MHz 15N NMR spectra of 15N-labeled Bacillus subtilis, Bacillus licheniformis, Staphylococcus auresu, Streptococcus faecalis, and Micrococcus lysodeikticus intact cells, isolated cells walls, and cell wall digests have been examined. The general characteristics of Gram-positive bacteria 15N NMR spectra and described and spectral assignments are provided, which allow in vivo 15N NMR to be applied to a wide range of problems in bacterial cell wall research. The qualitative similarity of the intact cell and cell wall spectra found in each bacteria allowed the 15 N resonances observed in the proton broad-band noise-decoupled 15N NMR spectra of intact cells to be assigned to cell wall components. Each of the five Gram-positive bacteria displayed a unique set of cell wall 15N resonances, which reflected variations in the primary structure of peptidoglycans and the amounts of teichoic acid and teichuronic acid in the cell wall, as well as the dynamic properties of the cell wall polymers. Spectral assignments of cell wall 15 N resonances assigned to teichoic D-Ala residues, teichuronic acid and acetamido groups, and peptidoglycan acetamido, amide, peptide, and free amino groups have been made on the basis of specific isotopic labeling and dilution experiments, comparison of chemical shifts to literature values, determination of pH titration shifts, cell wall fractionation experiments, and comparative analysis of the cell wall lysozyme digest spectra in terms of the known primary sequences of peptide chains. All the peptidoglycan 15N peptide resonances observed in the intact cells and isolated cell walls could be accounted for by residues in the bridge or crossbar regions of the peptide chains, which indicated that only the cross-linking groups had a high degree of motional freedom. Thermal- and pH-induced conformational changes around the cross-linking D-Ala residues were detected in the B. licheniformis cell wall lysozyme digest products. Comparison of the proton broad-band noise-decoupled and gated decoupled intact cell and cell wall 15N spectra indicated that broad-band proton decoupling resulted in nulling of cytoplasmic resonances and enhancement of the cell wall resonances by the 15N [1H5 nuclear Overhauser effect.

Bacillus↗
PubMed1979

Water permeability changes studied by 17O nuclear magnetic resonance during differentiation of Friend leukemia cells.

Water permeability of Friend leukemia cells was studied by 17O nuclear magnetic resonance during differentiation induced by dimethyl sulfoxide (Me2SO). While in noninduced cells water permeability was essentially constant during the growth period, in the Me2SO-induced cells there were two distinct periods at which the water permeability was increased by at least an order of magnitude. These periods correspond to approximately one doubling time and 6 days of growth. This change in water permeability is not due to direct interaction of Me2SO with the membrane but must be ascribed to structural changes in the membrane during the course of differentiation.

Animals↗
PubMed1979

Plasma amino acid turnover rates and pools in rabbits: in vivo studies using stable isotopes.

Gas chromatography--mass spectrometry of plasma amino acids has been used to determine the 15N enrichments of plasma glycine and alanine in rabbits in different metabolic states. Isotope-enrichment time-decay curves of plasma amino acids were linear over the course of the measurements after intravenous administration of a single dose of 15N-amino acid. Glycine and alanine pools and turnover rate constants were estimated from decay data. The effects of diurnal variation and fasting on glycine and alanine pool sizes, turnover rates, and flux in rabbits were studied to provide information on the effect of metabolic stress on amino acid kinetics in the whole body. The observations suggests that the transport of systemic glycine or alanine into the hepatocyte is under the control of a regulatory mechanism that compensates for decrease in the extracellular levels of the amino acids by enhancing the activity of the transport system. The volumes of the glycine and alanine pools were found to correspond to the extracellular space of rabbits, and the glycine and alanine pools can be identified as extracellular. We conclude that the plasma glycine and alanine 15N isotope-enrichment time-decay curves over the 1st h after a single intravenous dose of the amino acid represent mainly the hepatic uptake of glycine and alanine from the extracellular pool.

Alanine↗
PubMed1978

The determination of amino acid pool sizes and turnover rates by gas chromatographic mass spectrometric analysis of stable isotope enrichment.

Gas chromatography mass spectrometry has been used to determine the 15N enrichment of plasma glycine of rabbits at various times following the intravenous administration of 15N-glycine. These data were used to prepare isotope enrichment time decay curves for eleven individual animals. The slopes and intercepts of least squares lines that describe the decay curves were considerably more accurately than those reported in similar studies employing radioactive tracers. Individual glycine pool sizes (13.8-37.4 micronmoles per 100 g body wt), turnovers rates (2.66-3.36 pools h-1) and flux (50.4-99.7 micronmoles h-1 per 100 g body wt) were estimated from these parameters in a group of animals and compared with the literature values. These results demonstrate that low risk non-radioactive stable isotopes can be substituted for radioactive tracers in studies of human amino acid metabolism, with considerable saving in time and without loss in accuracy, when gas chromatography mass spectrometry is used to determine plasma amino acid and stable isotope enrichment.

Animals↗
PubMed1978

Effects of binding and bactericidal action of vancomycin on Bacillus licheniformis cell wall organization as probed by 15N nuclear magnetic resonance spectroscopy.

The effects of binding and the bactericidal action of vancomycin on the arrangement and mobilities of cell wall polymers in Bacillus licheniformis were investigated by (15)N nuclear magnetic resonance spectroscopy. The bactericidal action of vancomycin led to reduced mobilities of cell wall teichoic acid and teichuronic acid in surviving cells. The decrease in teichoic acid mobility was also observed upon binding of vancomycin to B. licheniformis cells and resulted from a specific interaction between the antibiotic and teichoic acid, rather than from electrostatic contraction of the cell wall. The reduction in teichuronic acid mobility appeared to be related either to the elastic contraction of the cell wall resulting from loss of cell turgor or to separation of the cell wall from the protoplast membrane. No spectral changes associated with cell wall autolysis or alterations in cell wall composition, amidation, and cross-linking were found in vancomycin-treated B. licheniformis cells. Binding of vancomycin to Micrococcus lysodeikticus cell walls led to a decrease in mobility of C-terminal d-alanine residues but was accompanied by an increase in the mobilities of other peptidoglycan residues. The possible contributions of changes in the arrangements of cell wall polymers to the lethal action of vancomycin is discussed.

Bacillus↗
PubMed1977

The dynamic structure of the Escherichia coli cell envelope as probed by 15N nuclear magnetic resonance spectroscopy.

Proton decoupled 15N NMR spectroscopy is shown to be a useful tool for probin the dynamic structure of the bacterial cell envelope. The proton decoupled 15N NMR spectra of Escherichia coli whole cells, cell envelopes and outer membranes were obtained and displayed resonances originating from protein side-chain groups, phosphatidylethanolamine, and peptidoglycan. Removal of phospholipids from the cell envelope resulted in a decrease in the motional freedom of peptidoglycan and cell envelope proteins. The mobility of the protein Arg side-chain groups is increased in the absence of peptidoglycan. These data provide insights into the effect of supramolecular organization on the dynamic structure of the E. coli cell envelope.

Bacterial Proteins↗
PubMed1977

Dynamic structure of whole cells probed by nuclear Overhauser enhanced nitrogen-15 nuclear magnetic resonance spectroscopy.

The proton-decoupled 15N Fourier transform nuclear magnetic resonance (NMR) spectra of 15N-enriched Escherichia coli, Bacillus licheniformis, baker's yeast, and Friend leukemic cells were obtained. The 15N NMR spectra of whole cells displayed 15N resonances originating from (i) protein backbones with lysine, arginine, and histidine side chains, (ii) ribonucleic acids, (iii) peptidoglycan, and (iv) phospholipids. Several additional amino and amide resonances were observed but not identified. In bacteria and yeast, the cell wall was found to be the site of a relatively mobile group of molecules, whose resonances dominate the proton-decoupled 15N NMR spectra of whole cells. 15N NMR chemical shifts and nuclear Overhauser effects have provided information on the in vivo structure of cell wall peptidoglycan. In Staphylococcus aureus the pentaglycine cross-bridge of cell wall peptidoglycan was found to have a random coil conformation. In B. licheniformis considerable segmental motional freedom was detected in teichuronic acid and peptidoglycan polysaccharide chains in the wall of the intact cell.

Bacillus↗
PubMed1976

A new functional approach to the surgical management of Pierre Robin syndrome: experimental and clinical report.

A functional and simple surgical method for treating the respiratory distress of the neonate affected by Pierre Robin syndrome is described. The base of the tongue is placed in an anterior position via a buried wire suture tied around the body of the hyoid. The method proposed in this paper fulfills the following: 1. It is physiologic since the infant is able to suckle and maintain its nutrition by preserving the function of the mobile portion of the tongue for deglutition. 2. Maintenance of the "pushing" action of the tongue stimulates growth of the mandible. 3. The anchoring wire is not exposed in the oral cavity and the risk of tissue breakdown and infection is eliminated. 4. This technique utilizes the stronger fibrous portion of the mid-tongue rather than muscle which "gives" more readily under pressure. 5. The shortest distance from the base of the tongue to the mid-hyoid provides the best mechanical advantage. 6. The suture, if need be, may be tightened at subsequent periods of time. Under Ketamin (Ketalan) anesthesia the tip of the tongue was held in the forward position. An 18 gauge stainless steel wire was inserted via a large curved needle through the midline of the posterior-most portion at the base of the tongue. The needle was directed anteriorly and inferiorly to emerge below the mid point of the inferior border of the hyoid bone. The opposite end of the wire was then tunneled submucosally to the anterior portion of the base of the tongue at foramen caecum, and directed inferiorly to emerge above the superior border of the mid-portion of the hyoid bone. Through a small skin incision opposite the body of the hyoid bone, both free ends of the wire were tied under tension around the body of the hyoid while pulling the base of the tongue forward. The skin incision was closed with a single nylon suture. A prosthetic obturator was used to close the cleft palate. The outcome was satisfactory with no morbidity.

Anesthesia↗
PubMed1976

A clinical-functional evaluation of facial paralysis.

A clinical-functional evaluation of facial paralysis is presented in order to suggest a uniform and standard classification. The outcome of this disease treated with various modalities may be similarly appraised by all medical disciplines. A score of 50 per cent is allotted to each of the main divisions of the facial nerve, namely, eye and oral commissure; 15 per cent is given to the symmetry in repose of the eye and oral commissure respectively; and 35 per cent to the sphincteric function of the orbicularis oculus and oris respectively.

Facial Paralysis↗
PubMedDate not supplied

Primary oat-cell carcinoma of head and neck.

Summary--A case of primary oat-cell carcinoma of the larynx in a 68-year-old white female is described, bringing to a total of three the reported cases in the world literature. The tumor is highly malignant and notorious for the speed with which it metastasizes. Treatment should be aggressive from the beginning. We believe that even for a localized tumor of this kind, a minimal procedure should be widefield laryngectomy with elective radical neck dissection even if clinically, nodes are not palpable. Since the tumor is highly radiosensitive, radiotherapy should be used postoperatively.

Aged↗