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101.
Application of arabinofuranosyl cytosine in the kinetic analysis and quantitation of DNA repair in human cells after ultraviolet irradiation. 总被引:2,自引:0,他引:2
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We have developed a technique whereby 3-h pulses of arabinofuranosyl cytosine (ara-C) and hydroxyurea (HU) are used to analyze the kinetics of repair with time after ultraviolet irradiation in human fibroblasts. We demonstrate that this technique offers a significant improvement over existing repair assays in its ability to visualize between 57 and 100% of all sites undergoing repair in a given period of time. In addition, kinetic analyses of repair are more easily made and yield more information than techniques such as repair replication or unscheduled DNA synthesis. We have also examined the nature of the inhibition event by ara-C and have determined that repair breaks accumulate in the presence of ara-C and HU only up to a certain time beyond which no further breaks appear. The time needed to reach this saturation point depends on the number of sites undergoing repair during the treatment time. This observation is discussed with respect to a possible mechanism of excision repair inhibition by ara-C and HU. 相似文献
102.
Explants of lung tissue from 19-day gestational age fetal rabbits were maintained in organ culture in medium with or without fetal calf serum for 1 to 11 days. Based on the results of biochemical and morphological studies it was apparent that the type II pneumonocyte differentiated in vitro at a time similar to that which occurs with maturation in vivo. The epithelial cells of the presumptive alveoli were undifferentiated at the start of incubation, but within 9 days developed increased amounts of Golgi apparatus and rough endoplasmic reticulum, many microvilli on the luminal surface and numerous lamellar bodies. Secreted lamellar bodies and tubular myelin figures were observed in the lumina of cultured explants. The incorporation of [3H]choline into phosphatidylcholine by lung tissue explants maintained in medium containing 10% fetal calf serum remained relatively constant for 7 days of incubation but thereafter increased two-fold. When explants were maintained in fetal calf serum-containing medium and cortisol (10?7M) or betamethasone (10?7M), the incorporation of choline into phosphatidylcholine was two to three times greater than that of explants maintained in serum-containing medium without cortisol. When explants of fetal lung tissue were incubated in the presence of cortisol without fetal calf serum there was no stimulatory effect of cortisol on phosphatidylcholine biosynthesis. Therefore, serum cofactors are necessary for the stimulatory effects of cortisol on fetal lung development. The specific activity of phosphatidate phosphohydrolase (PAPase) increased to very high levels during the culture period. In the presence of serum, cortisol or betamethasone had no effect on the specific activity of phosphatidate phosphohydrolase. 相似文献
103.
Spectrophotometric assays of esterases are sensitive, rapid, and quite specific when thioester substrates are used. Glycerophospholipids with thiophosphoester bonds may be useful as substrates for phospholipase C (EC 3.1.4.3). These have been made from mercaptoglycerol and mercaptoethanol. The thiols were oxidized to disulfides, acylated, and reduced with dithiothreitol. Phosphocholine derivatives were made by the classical methods for oxyphosphoesters. The phosphatidyl choline analogue was converted to the phosphatidyl ethanolamine analogue by transphosphatidylation with cabbage phospholipase D and ethanolamine. Structures were proved with enzymic hydrolysis, infrared spectra, TLC behavior, and elemental analyses. The synthesized compounds were rac-1-S-phosphocholine-2,3-O-didecanoyl-1-mercapto-2,3-propanediol, 1-S-phosphoethanolamine-2,3-O-didecanoyl-1-mercapto-2,3-propanediol, and 1-S-phosphocholine-2-O-hexadecanoyl-1-mercapto-2-ethanol. 相似文献
104.
105.
Frequency-Dependent Selection at the PGM-1 Locus of DROSOPHILA PSEUDOOBSCURA 总被引:4,自引:2,他引:2
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Frequency-dependent fitness was studied at the Pgm-1 locus of Drosophila pseudoobscura with respect to two fitness components: rate of development and larva-to-adult survival. The Pgm-1 locus is very polymorphic with only two alleles, Pgm-1100 and Pgm-1104, occurring at high frequencies. For each of these two alleles, 20 homozygous strains were obtained from a sample of 1,140 wild-inseminated females. First-instar larvae of the two genotypes were combined in a set of eight different frequencies: 0.0, 0.10, 0.25, 0.40, 0.60, 0.75, 0.90, and 1.0. Frequency-dependent fitness effects were observed for the two survival-related fitness components examined: larvae of the less common genotype develop faster and have a higher probability of survival than larvae of the more common genotype. The rate of survival at intermediate genotypic frequencies is similar to that in pure cultures. If selection acted solely as frequency-dependent effects on survival-related components of fitness, the equilibrium frequency of the Pgm-1100 allele would be 0.615 for a two-genotype system, which fits an observed frequency range for this allele in nature between 0.55 and 0.71. Experimentally created linkage disequilibrium was excluded from the experiment by using a large number of independent strains. It is nevertheless possible that the frequency-dependent selection may not affect the Pgm-1 locus per se, but may reflect a linkage disequilibrium present in the natural population. Even if this were the case, the frequency-dependent selection could affect the frequency of the Pgm-1 alleles in nature. 相似文献
106.
The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.This research was conducted at Yale University, Department of Ophthalmology and Visual Science, New Haven, Connecticut, USA, throughout which period A.W.S. was a John Simon Guggenheim fellow 相似文献
107.
delta5 desaturation of fatty acids in L-M cells 总被引:1,自引:0,他引:1
E N Lambremont T C Lee M L Blank F Snyder 《Biochemical and biophysical research communications》1978,80(4):813-818
L-M cells grown in a lipid-free medium containing 14C-labeled 9,12-linoleic acid incorporated most of this acid into glycerolipids as linoleic acid. Only a small amount (3%) was elongated to eicosadienoic acid. No Δ6 desaturation occurred. When the cells were incubated with 14C-labeled 8, 11, 14-eicosatrienoic acid, 22% of the activity was found in 5,8,11,14-eicosatetraenoic acid. Treatment of the cells for 24 hr with N-isopropylethanolamine, a choline analog, depressed this desaturation reaction to about 60% of control values. The identity of the tetraene product was established by two different chromatographic analyses of the fatty acid methyl esters. Location of the double bond at position C-5 was determined by ozonolysis and subsequent reduction of the ozonides to aldesters followed by gas-liquid chromatography. These results prove that L-M cells have a Δ5 desaturase and an elongation enzyme converting 18:2 to 20:2, but lack a Δ6 desaturase. 相似文献
108.
Michael E. Charness David B. Bylund Barbara S. Beckman Morley D. Hollenberg Solomon H. Snyder 《Life sciences》1976,19(2):243-250
Isoproterenol-stimulated adenylate cyclase activity in membrane preparations of reticulocyte-rich (90%) erythrocytes from phenylhydrazine-treated rats is 9 times greater than in untreated animals (1% reticulocytes); basal and fluoride-stimulated activities are also enhanced 2 and 4-fold respectively. In contrast, the number of β-adrenergic receptor sites detected by the binding of 125I-hydroxybenzylpindolol (125I-HYP) is increased only 40% in these same preparations. The dissociation constant (KD) of 125I-HYP and the IC50 of (-)-isoproterenol for receptor binding sites are unchanged, as is the EC50 of (-)-isoproterenol for activation of adenylate cyclase. The disproportionately large increase in the activity of the isoproterenol-sensitive adenylate cyclase, compared with the small increase in the number of 125I-HYP binding sites indicates that the functions of catecholamine recognition and consequent adenylate cyclase response can vary independently and suggest that the receptor and the cyclase may be autonomous molecular entities. 相似文献
109.
Rodney C. Baker Robert L. Wykle Jacalyn Schremmer Lockmiller Fred Snyder 《Archives of biochemistry and biophysics》1976,177(1):299-306
Stimulation of the desaturation of 1-alkyl-2-acyl-sn-glycero-3-phosphoethanolamine (GPE), which forms ethanolamine plasmalogens, by a component of the 105,000g supernatant has been previously reported. We have isolated the stimulatory protein and identified it as catalase. Purified rat liver catalase or commercial bovine liver catalase is as effective in stimulating microsomal 1-alkyl-2-acyl-GPE desaturation as the soluble proteins. The stimulatory effect of these proteins is eliminated by catalase inhibitors. It appears that catalase stimulates the desaturation of 1-alkyl-2-acyl-GPE by preventing inactivation of the enzyme system by H2O2 or a decomposition product of H2O2. The cytochrome b5 content and NADH oxidation are depressed in Fischer R-3259 sarcoma microsomes by H2O2; this effect is eliminated by catalase. However, since measurable inhibition of 1-alkyl-2-acyl-GPE desaturase by H2O2 still occurred in the presence of catalase, the inhibition by H2O2 cannot be explained solely on the basis of cytochrome b5 inactivation. The desaturation of stearoyl-coenzyme A, a reaction analogous in many respects to 1-alkyl-2-acyl-GPE desaturation, was also found to be stimulated by catalase. 相似文献
110.
Nitration of tyrosine has been investigated as a means for chemically introducing lanthanide chelating sites at known positions in proteins. The low-field portions of the 250-MHZ and 270-MHZ 1H nuclear magnetic resonance spectra of native and chemically modified bovine pancreatic trypsin inhibitor have been studied in the presence of lanthanide ions. Comparisons of spectral changes observed with native, mononitro (tryosine 10) and dinitro (tyrosines 10 and 21) derivatives enable these changes to be separately attributed to metal bound at nitrotyrosine 21, nitrotyrosine 10, or the set of five carboxyl groups. The pH dependence of Pr(III) and Eu(III) induced chemical shifts yields stability constants of 50 and 159 M-1 for the association between lanthanides and nitrotyrosines 10 and 21, respectively. Correlation times for the interactions with Gd(III) bound to specific nitrotyrosines are estimated from the induced line broadening of resonances of the nitrotyrosine ring protons. These stability constants and correlation times are used to determine the distances from the different metal binding sites to buried backbone NH protons having resolved resonances. Comparisons with distances in the x-ray crystal structure give assignments of the NH resonances to a small set of buried backbone NH's. 相似文献