共查询到20条相似文献,搜索用时 15 毫秒
1.
David Scicchitano Anthony E. Pegg 《Biochemical and biophysical research communications》1982,109(3):995-1001
The demethylation of O6-methylguanine in double stranded DNA catalyzed by rat liver O6-methylguanine-DNA transmethylase was found to proceed much more rapidly when the DNA substrate was methylated to a high extent. When the content of O6-methylguanine in DNA was equal to 1 in 2000 guanines, the reaction was 90% complete within 2 min, but when the content was 1 in 500,000 it required 27 min at 37°C. These results suggest that the repair protein either moves along the DNA substrate or else has little selectivity for binding specifically to the sites containing O6-methylguanine rather than to the normal DNA. The repair of O6-methylguanine in rat liver occurred at rates comparable to those seen with the substrates alkylated to low extents and was virtually complete within 3 hours. These results provide strong evidence that this protein is the factor responsible for O6-methylguanine removal and explain the wide variation in time courses reported in the literature since substrates methylated to greatly different extents have been used for such experiments. 相似文献
2.
Molecular characterization of a stable Flac plasmid 总被引:2,自引:0,他引:2
F L Macrina E Balbinder A Bassel 《Biochemical and biophysical research communications》1973,54(2):737-743
FS is a thermostable extrachromosomal element isolated in which is altered in its replication as compared to its precursor Fts114. Sedimentation of both these plasmids in alkaline sucrose gradients has indicated a difference in their sizes. Contour length measurements of open circular plasmid DNA molecules photographed in the electron microscope have revealed the estimated molecular weight of Fts114 to be 81 × 106 daltons while that of FS is 109 × 106 daltons. FS may carry a segment of chromosomal or cryptic plasmid DNA. 相似文献
3.
Dimers of escherichia coli F' factors 总被引:1,自引:0,他引:1
Covalently closed circular DNA dimers of several sex factors have been isolated. One of these, F′451, a dimer of F′450, has a molecular weight of 230 × 106 daltons. F′451 (λ) containing a λ prophage has a molecular weight of 260 × 106 and is probably the largest covalent closed circle of DNA yet reported. These dimers arise spontaneously and are of unknown origin and significance. 相似文献
4.
Characterization of mycoplasmatales virus DNA 总被引:4,自引:0,他引:4
The DNA of the group L1 virus, MVL51, was analyzed using alkaline sucrose velocity sedimentation, neutral and alkaline CsCl isopycnic sedimentation, and treatment of the DNA with nucleases. These treatments show that the viral chromosome is a covalently linked single-stranded DNA circle of molecular weight 2×106 daltons. 相似文献
5.
C I Hong A Nechaev C R West 《Biochemical and biophysical research communications》1979,88(4):1223-1229
Superior antitumor activity of 1-β-D-arabinofuranosylcytosine (ara-C) conjugates of prednisolone and prednisone against L1210 leukemic mice, based on ara-C content, has encouraged us to synthesize 5′-(cortisone-21-phosphoryl)-1-β-D-arabinofuranosylcytosine (I) and 5′-(cortisone-21-phosphoryl)-1-β-d-arabinofuranosylcytosine (II) by condensation of N4,2′,3′-triacetyl-1-β-d-arabinofuranosylcytosine 5′-monophosphate with cortisol and cortisone in the presence of N,N′-dicyclohexylcarbodiimide at room temperature followed by removing the acetyl groups in 2 N methanolic ammonia in 20% yield. The conjugates I and II inhibited the growth of L1210 by 50% (ED50) at 0.25 μM and 0.07 μM, respectively, while ara-C showed ED50 0.1 μM. However, the conjugates I and II exhibited 287% and 238% of at 50 mg/kg/day × 5 doses against L1210 leukemic mice, respectively, while ara-C at 25 mg and 50 mg/kg/day × 5 gave the respective 127% and 110% of . 相似文献
6.
K Shimada T Nakamura S Maeda Y Takagi 《Biochemical and biophysical research communications》1977,75(3):659-666
Ampicillin-resistant colonies that did not utilize galactose appeared sporadically in cultures of galactose genedeleted K-12 cells containing colicin E1 factor carrying genes for galactose utilization and ampicillin resistance. Most of these colonies contained small plasmid DNAs. These plasmids existed as monomer DNAs within K-12 cells and formed a series of covalently closed circular DNA molecules ranging in size from 6.3 × 106 to 15.1 × 106 daltons. The use of these plasmid DNAs was discussed. 相似文献
7.
[3 H] Estradiol-17β-succinyl bovine serum albumin conjugate ([3H]-E2-BSA) was synthesized with a specific activity of 1.92 × 107 cts/min/mg. The conjugate was administered iv to ovariectomized rats and the quantity of free [3H] steroid in the uterus was determined. Radioactive material was detected in all of the subcellular fractions of the uterus and identified as estradlol-17β. Similar subcellular distribution of the radioactivity was observed when [3H]E2-BSA was added to uterine homogenate. Free estradlo1-17β was released when the conjugate was Incubated with rat uterine homogenate or with serum. The results of the present study suggest that E2-BSA is hydrolyzed and under conditions. It is recommended that the stability of a hormone-protein conjugate be established before use. 相似文献
8.
The reactivity of rat liver glutathione (GSH) peroxidase with two hydroperoxides was determined using integrated rate equations. The bimolecular rate constant for the reaction of GSH peroxidase with linoleic acid hydroperoxide is approximately four times the rate constant with cumene hydroperoxide. The reactivity toward reduced glutathione is not altered by different hydroperoxides. The for lipid hydroperoxide in rat liver is approximated at 9.5 × 10?5 min. 相似文献
9.
Neurotransmitter storage vesicles were isolated from rat brain by differential centrifugation and the uptake of (?) 3H-norepinephrine was determined . Uptake showed a marked temperature dependence, an absolute requirement for ATP-Mg2+, and was inhibited by reserpine. Uptake was linear for 5 min at 30°, but not at 37°. The uptake was saturable and displayed a single Km value of 4 × 10?7 M. Other phenylamines and indoleamines displayed competitive inhibition of norepinephrine uptake; the affinities followed the rank order: reserpine>harmaline>serotonin>epinephrine> dopamine>norepinephrine>metaraminol. Uptake was reduced in vesicles isolated from rats treated intracisternally with 6-hydroxydopamine but not from rats treated with 5,6-dihydroxytryptamine, suggesting that most of the uptake occurs in catecholaminergic, and not serotonergic, vesicles. This method provides a ready characterization of pharmacologic effects on rat brain storage vesicle properties, as demonstrated by the prompt and complete inhibition of uptake after administration of reserpine . 相似文献
10.
Benzodiazepine receptors were labeled with [3H] diazepam following intravenous injection in rats. Binding of [3H] diazepam to rat forebrain membranes was displaceable by co-injection of clonazepam or the pharmacologically active enantiomers of two benzodiazepines, B9 and B10, but was not displaced by equal doses of the pharmacologically in-active enantiomers. Binding of [3H] diazepam was bserved in kidney, liver, and abdominal muscle, but was not stereospecifically diplaced in any peripheral tissue studied. The regional distribution of benzodiazepine receptors in brain was uneven, with specific [3H] diazepam binding being highest in the cerebral cortex and lowest in the ponsmedulla. Preliminary studies of the subcellular distribution of [3H] diazepam binding demonstrated highest specific binding to synaptosomal membranes. These data demonstrate the feasibility of labeling benzodiazepine receptors in rat brain . 相似文献
11.
M S Soloff 《Biochemical and biophysical research communications》1975,66(2):671-677
Particles from rat oviduct homogenates sedimenting between 1,000 × g for 10 min and 48,000 × g for 30 min bound [3H]oxytocin . The apparent Kd for oxytocin binding to high affinity sites in particles prepared from estrogen-treated rats was 1.8 × 10?9 M. About 215 fmoles of oxytocin were bound per mg of particulate protein. Oviducal preparations from untreated rats had about 25% the affinity for oxytocin of preparations from estrogen-treated rats. Oxytocin analogues were bound to oviducal particles in the same rank order as their uterotonic potencies: (desamino)oxytocin > (4-threonine)oxytocin > oxytocin > (8-lysine)vasopressin ? desaminotocinol. No oxytocin binding could be shown with the particulate fractions from rat ovary. The binding of oxytocin to the oviduct and uterus are similar in affinity, number of binding sites, ligand specificity, and the increase in response to estrogen treatment. 相似文献
12.
Linear, size-heterogenous mitochondrial DNA from was cleaved by the restriction endonuclease Eco R I into eleven specific fragments. According to their contour lengths the fragments have molecular weights between 1.1 and 14 × 106. The sum of the fragments lengths is identical with the contour length (19.8 μm, 41 × 106 daltons) of the few circular molecules detectable in purified DNA preparations.The results suggest sequence homogeneity of mitochondrial DNA and further demonstrate that restriction enzymes can be used to establish a physical map of an unspecifically-fragmented DNA molecule. 相似文献
13.
The effect of morphine sulfate (MS) on adenylate cyclase (AC) and phosphodiesterase (PDE) activities in the rat striatum was investigated. MS produced a dose-dependent increase in basal AC activity and did not alter sodium fluoride-induced stimulation both (7.5–30 mg/kg, 1 hr pretreatment, i.p.) and (1–100μM). , when submaximal effective concentrations of dopamine and MS were combined, there was an additive effect. However, administration of MS did not alter dopamine-induced stimulation of AC activity. MS, and inhibited PDE activity in a dose-dependent manner only with the high substrate concentration (3.3 × 10−3M cyclic AMP). Preliminary results from this study indicate that morphine affects the cyclic AMP system. 相似文献
14.
A study was made of the phosphorylation of chromatographically purified histone H1 subfractions from the liver of premetamorphic tadpoles (). Two H1 subfractions were obtained which differed in terms of net incorporation of [32P]phosphate . Analysis of N-bromosuccinimide cleavage products further revealed that the two subfractions also differed in the relative distribution of [32P]phosphate in N- and C-terminal regions of the molecule. Incorporation of [32P]phosphate into both regions of the molecule occurred virtually exclusively in serine residues. 相似文献
15.
The biosynthesis of 2-methylalkanes was studied in the crickets and . Labelled acetate, valine, and isobutyric acid were incorporated into the cuticular hydrocarbon of at levels of 6.0 ± 1, 6.5 ± 2, and 1.5 ± 0.7 percent respectively. The hydrocarbons of this insect are 20 percent 2-methylalkanes, primarily of even numbered carbon chain lengths, and 80% n-alkanes. Of the label incorporated into the hydrocarbon fraction, 28 ± 2 percent of sodium [1-14C] acetate, 98 ± 1 percent of L-[G-3H] valine, and 75 ± 10 percent of [1-14C] isobutyric acid were incorporated into the 2-methylalkanes. This suggests that valine is converted to isobutyric acid and is incorporated into the even numbered carbon chain length 2-methylalkanes during the initial stages of chain elongation. Similar data obtained in suggests that leucine is converted to isovaleric acid which is then incorporated into the odd numbered carbon chain length 2-methylalkanes. 相似文献
16.
C.Channa Reddy Nan-qian Li Chen-Pei D. Tu 《Biochemical and biophysical research communications》1984,121(3):1014-1020
A new glutathione -transferase has been purified to homogeneity from 105,000 × g supernatant of Sprague-Dawley rat liver homogenates. The purified enzyme exhibited specific activities of approximately 1.8, and 0.12 μmoles. min?1. mg?1 toward 1-chloro 2,4-dinitrobenzene and cumene hydroperoxide respectively. The SDS gel electrophoresis data on subunit composition revealed that the new transferase is composed of two subunits with an identical Mr of 24,400 (Yα Family). Our translation experiments with rat liver poly(A) RNAs and substrate specificity data suggest that this subunit is different from the previously reported Ya, Yb and Yc subunits of rat liver glutathione -transferases. Comparatively, the new isozyme showed significant activity toward 1,2 epoxy-3-(P-nitrophenoxy)-propane, ethacrynic acid and P-nitrophenyl acetate, 0.4, 0.34 and 0.18 μ moles. min?1. mg?1 respectively. 相似文献
17.
Transfer of phospholipids between the endoplasmic reticulum and mitochondria in rat hepatocytes in vivo 总被引:1,自引:0,他引:1
I Eggens C Valtersson G Dallner L Ernster 《Biochemical and biophysical research communications》1979,91(3):709-714
The transfer of phospholipids from the endoplasmic reticulum to the inner mitochondrial membrane was investigated by pulse labeling . With [3H]glycerol microsomal phosphatidylethanolamine and phosphatidylcholine were rapidly labeled during the first 30 min; while maximum incorporation into the inner mitochondrial membrane occurred only after about 5 hours. It appears that the transfer of these phospholipids between the two membrane compartments is a relatively slow process. 相似文献
18.
H P Moore P R Hartig W C Wu M A Raftery 《Biochemical and biophysical research communications》1979,88(2):735-743
Rapid efflux of 22Na from within closed vesicles derived from electroplax membranes has been studied as an assay of acetylcholine receptor functionality. The most highly purified membrane preparations contained major polypeptides of M.W. 43 and 90 × 103 daltons in addition to the four peptides characteristic of the acetylcholine receptor (40, 50, 60, 65 × 103 daltons). Removal of these extra peptides by base extraction did not significantly alter the characteristics of carbamylcholine induced 22Na efflux: the agonist dose response curve was similar, preequilibration with agonist caused desensitization, the irreversible antagonist α-Bungarotoxin blocked the efflux and the reversible blockade by the neurotoxin perhydrohistrionicotoxin was also retained. The dose response curve for perhydrohistrionicotoxin corresponded closely to its known binding characteristics for base extracted membranes. 相似文献
19.
The effects of low temperature and chloroquine on 125I-insulin degradation by the perfused rat liver
Low temperature and the lysosomotropic agent, chloroquine, were used to study the degradation of 125I-insulin in a perfused rat liver. Insulin (1.5 × 10?9m) was removed from the perfusate at 35 °C with a of 12 min, and this process was slowed to 35 min at a temperature of 17 °C. Essentially no degradation of 125I-insulin took place in the liver at 17 °C. After 90 min at that temperature 64% of the liver radioactivity had accumulated in the microsomal fraction of the tissue homogenate, while at 35 °C 60% of the radioactive material was in the supernatant fraction. Greater than 80% of the supernatant radioactivity was acid soluble. Rapid warming of a 17 °C-treated liver to 35 °C allowed the accumulated 125I-insulin in the microsomal fraction to be degraded to acid-soluble products in the normal manner. Chloroquine (0.2 mm) also caused the liver to degrade insulin more slowly. At 60 min after adding 125I-insulin to the chloroquine-treated liver, 50% of the radioactivity in the tissue was still present in the lysosome-rich fraction of the homogenate, while less than 10% was in this fraction in a control liver. The effects of low temperature show transfer of insulin to its degradative site is rate limiting for hormone catabolism and the inhibition by chloroquine suggests lysosomes have a role in insulin degradation by the liver. 相似文献
20.
Kinetic properties of rat hepatic prolactin receptors 总被引:1,自引:0,他引:1
Binding of 125I-labelled ovine prolactin to female rat liver membranes underequilibrium conditions showed an apparent Kd of 200 pM, and a Hill coefficient of 1.0. The association rate was second order, with a rate constant K1, of 2.1 × 107, 1.4 × 107, 1.2 × 107 and 4 × 106 M?1. min?1 at 37, 30, 24 and 4° respectively. At 24° there were two components to the dissociation; a faster phase with K?1=1.26 × 10?2. min?1 () and a slower phase with K?1=1.103 × 10?3. min?1. The apparent Kd (from K?1K1) was 1.05 nM for the faster phase and 87.5 pM for the slower phase. These data suggest that there is a conformational change following hormone binding which results in an increased receptor affinity, which effectively prevents release of bound hormone. 相似文献