Effect of lipophilicity of nitroimidazoles on radiosensitization of hypoxic bacterial cells in vitro.
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The effect of radiosensitization of hypoxic bacterial cells by 9 nitroimidazoles was measured in the bacterial strains E. coli AB 1157 and S. lactis 712. Seven of these compounds were similar to misonidazole in their redox properties, but differed widely in their lipophilicites. The dependence of sensitization enhancement on reduction potential was similar to that reported in mammalian cells. The efficiency of sensitization was similar for compounds of low lipophilicity, but increased if the octanol: water partition coefficients of the compounds were higher than about 3.5. With one compound, otherwise similar to misonidazole, the increased lipophilicity led to about one order of magnitude lower concentration achieving the same degree of radiosensitization. (+info)
An investigation of the 16-S RNA binding sites of ribosomal proteins S4, S8, S15, and S20 FROM Escherichia coli.
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The RNA binding sites of four 30-S ribosomal subunit proteins from Escherichia coli, namely S4, S8, S15, and S20 were prepared from reconstituted single protein - 16-S-RNA complexes by mild enzymic digestion of non-protected RNA regions. Oligonucleotide fingerprints of the protected RNA regions were obtained and their positions were located within the 16-S-RNA sequence. They were not completely contiguous regions of RNA; oligonucleotides had been excised from each of them. The binding sites of S4 and S20, and those of S8 and S15 showed overlapping. The specificity of the RNA binding sites was confirmed by a reconstitution method. (+info)
The primary structure of the major cytoplasmic valine tRNA of mouse myeloma cells.
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This paper describes the derivation of the primary structure of the major valine tRNA in the cytoplasm of mouse myeloma cells. Approximately 75% of the nucleotide sequence of this tRNA is also shared by the tRNA1-Val of yeast, this homology serving as a further indication of the extreme conservation of the structures of the tRNAs of different eukaryotic organisms. A novel feature of mouse myeloma tRNA1-Val is its loop IV sequence: -U-PSI-C-G-M1A-A-A-. This particular loop IV sequence has not previously been found in a tRNA structure. In addition, tRNA1-Val possesses some unusual nucleoside modifications. 5-Methyluridine (T) was not found to occur within loop IV of this tRNA, although this minor nucleoside is also absent from certain other mammalian tRNAs. Only one other tRNA, mammalian tRNAf-Met, has been found to possess 2-methylguanosine (m2G) in the position between the (b) and (c) stems of the cloverleaf. Numerous tRNAs have m2-2G in this location, and it would appear that the second methylation of this guanosine is characteristically absent from certain mammalian tRNA species. (+info)
The gentamicin antibiotics. 6. Gentamicin C2b, an aminoglycoside antibiotic produced by Micromonospora purpurea mutant JI-33.
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A mutant strain of Micromonospora purpurea, designated var. JI-33, produced an antibiotic complex consisting primarily of gentamicin C1a. A further product of this fermentation was identical to a very minor component isolated from the fermentation of the parent organism and named gentamicin C2b. Physical measurements indicated its structure to be 6'-N-methylgentamicin C1a and this was confirmed by synthesis from gentamicin C1a. The in vitro antibacterial activity of gentamicin C2b was very similar to that of the gentamicin C complex. Antibiotic XK-62-2, produced by Micromonospora sagamiensis, appears to be identical to gentamicin C1b. (+info)
A new prodiginne (prodigiosin-like) pigment from Streptomyces. Antimalarial activity of several prodiginnes.
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Two prodigiosin-like pigments from Streptomyces sp. were shown to be undecylprodiginine (i) and butylcycloheptylprodiginine (v). The antimalarial activity of five prodiginine pigments is given. (+info)
Further investigation of the role of calcium in human lens protein aggregation.
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High-molecular-weight (HMW) protein from human cataractous lenses, isolated by differential centrifugation, was deaggregated in 7M urea and then reaggregated in either the presence or absence of 10 mM CaCl2. Over 90% of the material reaggregated in the presence of calcium appears to have a size greater than 50 X 10(6) daltons. By contrast, only 20% to 25% of the material reaggregated in the absence of calcium has molecular weight greater than 50 X 10(6) daltons. Disulfide formation during reaggregation is unlikely in the latter experiment, since the addition of 50 mM mercaptoethanol caused no change in results. About 60% to 70% of the low-molecular-weight (LMW) protein fraction deaggregated in 7M urea buffer can be converted to HMW species in the presence of 10 mM CaCl2, when the deaggregating agent is removed. However, only 5% to 10% of this protein is converted to HMW species if the deaggregation step is eliminated. Experiments with 45 Ca indicate that whereas calcium is necessary for the formation of the HMW aggregates, only one calcium per approximately 5 X 10(5) daltons remains bound in the reaggregated material. The data suggest that although calcium may be required to induce aggregation to HMW species, it is not required to stabilize such macromolecules. SDS-polyacrylamide gel electrophoresis of the HMW species formed upon reaggregation of the dissociated HMW species with calcium indicates the presence of all the major polypeptide subunits of the original HMW species present in the lens; however, reaggregation in the absence of calcium yields HMW species lacking in the 9600 dalton component. (+info)
Tertiary hydrogen bonds in the solution structure of transfer RNA.
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The high resolution nuclear magnetic resonance (NMR) spectra of hydrogen-bonded protons in four tRNAs have been studied at 270 MHz. The relative intensity of the resonances between -11 ppm and -15 ppm of Escherichia coli tRNA1-Va1 indicate that there are 26 plus or minus 3 protons, while only 20 are expected from secondary structure Watson-Crick hydrogen bonds inthe cloverleaf structure. Several possible candidates for these extra resonances are suggested by tertiary interactions observed in recent crystallographic studies. Of the four tRNAs studied, three, e.g., E. coli tRNA1Va1, E. coli tRNA-Arg and E. coli tRNA-Phe have one "GU pair" in their cloverleaf structure, while the fourth, yeast tRNA-Asp,has three "GU pairs" and one "G pair". Correlating these with the NMR spectra in the -10 ppm to -11 ppm region allows us to conclude that the "GU pairs" are not hydrogen-bonded by tautomerization to the lactim form. At the very low field region, near -14.9 ppm, the three E. coli tRNAs show a single resonance which is attributed to the 4-thiouracil 8 to adenine 14 hydrogen bond of the tertiary structure, by analogy with the recent crystal structure of yeast tRNA-Phe. This assignment is confirmed by the disappearance of this resonance after treatment with cyanogen bromide. (+info)
Change of spontaneous reaction of glue and lipiodol mixture during embolization after the addition of tungsten powder: in vitro study.
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BACKGROUND AND PURPOSE: We have noted that glue-Lipiodol mixtures harden prematurely in the catheter during embolization of brain arteriovenous malformations. However, we observed that hardening of this embolic material does not occur when tungsten powder is added to the glue mixture. In order to clarify the effect of tungsten powder on the glue mixture, we evaluated the reaction time and hardness of the glue mixture in vitro after the addition of tungsten powder. We also measured the pH of the tungsten solution. METHODS: Six lots of Lipiodol and three lots of Histoacryl Blue were mixed in a 5-cc bottle with a 50% to 25% glue concentration (glue:Lipiodol = 1:1 to 1:3) and this mixture was observed for 2 weeks. The hardness of the polymerized glue mixture was categorized as liquid, gel, semi-solid, or solid. Various series of experiments were performed after the addition of tungsten powder (0.2 g) and blood (a drop) into the glue mixture. We also separately mixed tungsten and tantalum powder in tubes, each with 5 mL of distilled water, and then measured the pH of these three times. The mixed amounts of tungsten and tantalum ranged from 0.1 to 0.5 mg. RESULTS: In a 50% glue concentration, the glue mixture turned into a solid cast within 48 hours. In a 25% concentration, the glue mixture turned into gel within 24 hours. The casts became solid in the 50% and gelled in the 25% concentration, and solid or gel in 28% and 33% glue mixture concentrations. The addition of tungsten powder to 50% and 25% glue mixture concentrations caused the glue mixtures to remain in a liquid state for 2 weeks regardless of the Lipiodol products used. Measurement of acidity achieved using a pH meter in 5 cc of distilled water with tungsten powder (0.1 to 0.5 g) revealed a change of pH from 3.5 to 2.6 according to the amount of tungsten added. Tantalum revealed weak acidity, with a pH range from 6.4 to 5.7. The addition of blood immediately caused the mixture to become solid in 50% and semi-solid in 25% glue concentrations. CONCLUSION: The reaction time of the glue mixture differed according to the lot number of the Lipiodol. The addition of tungsten powder appeared to prevent premature cast formation by decreasing the pH with a mechanism similar to that of adding acetic acid. (+info)