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1.
S Friedman 《Biochemical and biophysical research communications》1979,89(4):1328-1333
5-Azacytidine, when added to growing K12, causes a decrease in DNA methylation assayed . This decrease is greater when DNA is used as substrate than when calf thymus DNA is used. The decrease in activity is not due to the inhibition of protein synthesis caused by this drug, since neither chloramphenicol nor rifampin causes a decrease in enzyme activity. The effect is specific for the DNA(cytosine-5)methylase; the methylation of adenine is not affected. The concentration of drug that inhibits the DNA methylase by 50% is the same concentration that inhibits cell growth by 50%. 相似文献
2.
J Germershausen D Goodman E W Somberg 《Biochemical and biophysical research communications》1978,82(3):871-878
RNA (guanine-7) methyltransferase, partially purified from mycelia, catalyzed the transfer of the methyl group from S-adenosylmethionine to the 5′ terminus of both poly A(+) RNA and reovirus unmethylated mRNA. RNase T2 digestion of the methylated poly A(+) RNA from yielded the “cap” structures m 7G(5′)pppAp and m 7G(5′)pppGp in a ratio of 2:1 respectively. RNase T2 digestion of the methylated reovirus mRNA yielded m 7G(5′)pppGp exclusively. The absence of mRNA 2′-0-methyltransferase activity in the enzyme preparation is consistent with the absence of 2′-0-methylation in mRNA [Seidel, B. L. and Somberg, E. W. (1978) Arch. Biochem. Biophys. , 108–112]. This is the first isolation of an eucaryotic, cellular RNA (guanine-7) methyltransferase that has been shown to methylate homologous substrate. 相似文献
3.
Strand resealing in the excision repair of 5,6-dihydroxy-dihydrothymine in osmium tetroxide oxidized polyd(A-T) by crude extracts is accomplished by polynucleotide ligase. Osmium tetroxide oxidized polyd(A-T)_serves as a chemically well defined model substrate containing damage of the kind introduced into DNA by ionizing radiation. In the first incision step of excision repair approximately one endonucleolytic nick is introduced into the polymer by extracts of endoI? and endoI?A6? per ring damaged thymine residue removed. 相似文献
4.
The 2′,3′-dialdehyde of ADP, obtained by periodate oxidation of ADP, inhibited the hydrolytic activity of the purified Ca2+, Mg2+-activated ATPase of . In the initial stages of the reaction inhibition was due to the reaction of 1 mol inhibitor/active site. When non-specific labelling of amino groups by the dialdehyde was lowered by the simultaneous presence of 15 mM ATP in the reaction mixture, 3 mol “ATP-protectable” binding sites/mol ATPase were found. “ATP-protectable” binding of the dialdehyde was not observed when the hydrolytically inactive ATPase of an mutant of was used although binding of the inhibitor to non-protected amino groups still occurred. This suggests that the mutant ATPase is unable to bind ATP or that the amino groups with which the dialdehyde reacts in the native enzyme are absent or masked. 相似文献
5.
Compound 102804 isolated from has been found to be a potent inhibitor of the N5-methyltetrahydrofolate-homocysteine transmethylase isolated from B. This inhibition was noted when 102804 was added to the enzyme reaction mixture after the reaction started or concurrently with the preparation of the mixture. Chemically inactivated 102804 has no activity as an inhibitor of this enzyme system. 相似文献
6.
Oswald G. Baca James W. Bodley 《Biochemical and biophysical research communications》1976,70(4):1091-1096
70S ribosomes uniformly labeled with 32PO4 were subjected to varying doses of u.v. radiation and then to the combined action of the RNases A and T1. Following these treatments the ribosomal proteins were separated by trichloroacetic acid precipitation from the noncovalently attached RNA degradation fragments. Subsequent two-dimensional gel electrophoresis and autoradiography of these proteins revealed that significant 32PO4 was associated with unique ribosomal proteins, L2 was among these. 相似文献
7.
C. Schneller J.M. Schneller A.J.C. Stahl 《Biochemical and biophysical research communications》1976,70(3):1003-1008
Whereas m1G, m2G, m22G, m7G, T, m1A, m5C and Cm methylase activities were found in total cell enzyme of using under-methylated tRNA and B tRNA in reaction with or without Mg++, only m1G, m2G, m22G and T methylases occurred in mitochondria. Mitochondrial and cytoplasmic tRNA cannot be methylated by their homologous enzymes; only mitochondrial tRNA can be methylated in a heterologous reaction by total cell enzyme with formation of T, m5C, m1A and low amounts of m2G and m22G. 相似文献
8.
The amino acid sequences of pyridoxal-binding tetrapeptide and the NH2-terminal portion of aspartate transaminase from B were analyzed and compared with those of the corresponding parts of the cytosolic and mitochondrial isozymes from pig heart. After borohydride reduction and chymotryptic digestion of the enzyme, a pyridoxal-containing peptide was isolated, showing the sequence, Ser-Lys(Pxy)-Asn-Phe, identical with that of the cytosolic isozyme. The NH2-terminal sequence was determined up to 33 residues with a liquid phase sequence analyzer. Nearly the same degree of homology was observed among the NH2-terminal sequences of the three aspartate transaminases. 相似文献
9.
S Nasu F D Wicks S Sakakibara R K Gholson 《Biochemical and biophysical research communications》1978,84(4):928-935
Two proteins (A and B) from are required for the synthesis of the NAD precursor quinolinate from aspartate and dihydroxyacetone phosphate. Mammalian liver contains a FAD linked protein which replaces B protein for quinolinate synthesis. D-aspartic acid but not L-aspartic acid is a substrate for quinolinic acid synthesis in a system composed of the B protein replacing activity of mammalian liver and A protein. In contrast the B protein- A protein quinolinate synthetase system requires L-aspartic acid as substrate. The previous report that L-aspartate was a substrate in the liver- system was due to contamination of commercially available [14C]L-aspartate with [14C]D-aspartate. These and other observations suggest that liver B protein is D-aspartate oxidase and B protein is L-aspartate oxidase. 相似文献
10.
O Brown F Yein D Boehme L Foudin C S Song 《Biochemical and biophysical research communications》1979,91(3):982-990
Quinolinate phosphoribosyl transferase was rapidly inactivated in exposed to hyperbaric oxygen. The enzyme is essential for de novo biosynthesis of NAD in and man. Because of its sensitivity and essentiality, inactivation of this enzyme is proposed as a significant mechanism of cellular oxygen toxicity. Niacin which enters the NAD biosynthetic pathway below the oxygen-poisoned enzyme provided significant protection against the decrease in pyridine nucleotides and the growth inhibition from hyperoxia in and could be useful in cases of human oxygen poisoning. 相似文献
11.
Two forms of glutamine synthetase in free-living root-nodule bacteria. 总被引:23,自引:0,他引:23
Cell-free extracts of 61A76 contain two forms of glutamine synthetase (EC 6.3.1.2) which can be easily separated by isoelectric focusing. The more acid form (pI = 5.4), like the enzyme from , is stable at 50° and catalyses an ADP-dependent transferase reaction, whose inhibition by excess Mg++ can be relieved by snake venom phosphodiesterase. The more alkaline form (pI = 6.1) is labile at 50°, and catalyses and ADP-dependent transferase reaction which is strongly inhibited by Mg++ regardless of phosphodiesterase treatment. We have also observed the two forms of the enzyme in a nitrogenaseless mutant of 61A76, and in other strains of rhizobia, but only the acid form in W, OP, and M 51A. 相似文献
12.
S G O'Neal D B Rhoads E Racker 《Biochemical and biophysical research communications》1979,89(3):845-850
Vanadate is a potent inhibitor of the Ca2+-ATPase activity of sarcoplasmic reticulum in the presence of A-23187. The purified enzyme is sensitive to vanadate even in the absence of the ionophore. Ca2+ and norepinephrine protect the enzyme against inhibition of vanadate. The nonspecificity of vanadate is emphasized by the finding of inhibition of several other ATPases including the Ca2+Mg2+-ATPases of the ascites and human red cell plasma membranes, Mg2+-ATPase of the ascites plasma membrane, and the K+-ATPases of and hog gastric mucosal cell membranes. The ascites plasma membrane Ca2+-ATPase (an ecto ATPase) and mitochondrial ATPase are not inhibited by vanadate. 相似文献
13.
Regulation of the basal and cyclic AMP-stimulated rates of glycogen synthesis in Escherichia coli by an intermediate of purine biosynthesis 总被引:2,自引:0,他引:2
M P Leckie S E Porter V L Tieber D N Dietzler 《Biochemical and biophysical research communications》1981,99(4):1433-1442
In an abrupt increase in the rate of glycogen synthesis occurs at the onset of total nitrogen starvation. We present here both and data indicating that this increase occurs because of the loss of a nitrogen-containing intermediate of purine biosynthesis (apparently 5-aminoimidazole-4-carboxamide ribonucleotide) that inhibits glycogen synthesis. We also show that this inhibitory intermediate antagonizes the stimulation of glycogen synthesis by 3′,5′-cyclic AMP. The uncovering of the regulation of glycogen synthesis by this inhibitor apparently provides the first link in understanding the 23-year-old observation of a reciprocal relationship between growth rate and glycogen accumulation in . 相似文献
14.
Chemically formylated Met-tRNAmMet and Met-tRNAfMet species from and yeast were tested for their capacity to serve as chain-initiators in a cell-free system from . In the presence of R 17 mRNA, initiation factors and ribosomes, all four Met-tRNAs could form functional initiation complexes as measured by ribosomal binding kinetics, fMet-puromycin formation and synthesis of a dipeptide fMet-Ala. Unformylated Met-tRNAfMet from displayed significantly less activity as a peptide chain-initiator than the formylated Met-tRNAmMet species from and yeast. Although the latter tRNAs were less effective initiators than the “physiological” initiator tRNAs, the data seem to indicate that a blocked α-amino group represents the major token of identification by which Met-tRNA is admitted to function in peptide chain initiation. 相似文献
15.
The replication defective transducing phage λp3 carries a portion of the operon in the 2 region of the lambda phage. This operon segment contains the promoter, the operator, and the β-galactosidase gene, but does not contain the repressor gene. The gene can be expressed from both the inserted promoter and the phage promoter. When strain 594 (?, +) or JC6256 (Δ) is infected by λp3 in the absence of additional cyclic AMP, β-galactosidase synthesis is shown to be expressed from the phage promoter. When 594 (λ+) or JC6256 (λ+) is infected by λp3 in the presence of additional cyclic AMP and IPTG, β-galactosidase synthesis is shown to be expressed from the inserted promoter.The ability to separate the phage promoter from the inserted promoter for β-galactosidase expression will simplify the interpretation whenever λp5 is used. 相似文献
16.
G Tunnicliff 《Biochemical and biophysical research communications》1980,97(3):1024-1030
Crude lysates from a strain of enterotoxigenic have been shown to catalyse the incorporation of [32P] from [adenylate-32P] NAD+ into an 11,000 dalton protein in rat liver membranes. [32P] incorporation paralleled adenylate cyclase activation and the results suggest that the mechanism of action of the heat-labile enterotoxin may involve ADP-ribosylation of an intracellular acceptor protein. 相似文献
17.
Neomycin inhibits DNA dependent DNA and RNA synthesis catalyzed by DNA polymerase I and RNA polymerase from . The effect of the antibiotic is more pronounced towards DNA synthesis. The inhibition of DNA synthesis is competitive with template DNA, does not reverse with excess deoxynucleoside triphosphate, Mg2+ or enzyme DNA polymerase I. Neomycin does not reduce the number of potential 3′ -OH end or primer. It seems to shorten the size of the newly formed polynucleotide. 相似文献
18.
C R Geren L M Geren K E Ebner 《Biochemical and biophysical research communications》1975,66(1):139-143
A thermostable protein that strongly inhibits the soluble D-alanine carboxypeptidase was isolated from a cell-free extract of . The inhibitor was purified 140-fold by heat treatment, selective precipitation at pH 4.5, ion exchange chromatography on DEAE-cellulose and gel chromatography on Sephadex G-100. Inhibition of soluble D-alanine carboxypeptidase by this inhibitor is reversed by cations such as Mg++ or Na+ and abolished by digestion of the inhibitor with proteolytic enzymes. The inhibitor does not affect either the particulate D-alanine carboxypeptidase of or the growth of the bacteria. 相似文献
19.
R W Fuller H D Snoddy K W Perry B W Roush B B Molloy F P Bymaster D T Wong 《Life sciences》1976,18(9):925-933
Quipazine, 2-(1-piperazinyl)-quinoline, is a drug that has been reported to stimulate serotonin receptors in brain. We therefore studied the effect of quipazine on several parameters of serotonin metabolism in rat brain. Quipazine caused a slight, dose-related elevation of serotonin levels and decrease in 5-hydroxyindoleacetic acid levels for 2–4 hrs after it was administered. The decrease in 5-hydroxyindoleacetic acid levels was probably due primarily to a depression of 5-hydroxyindole synthesis, since quipazine also decreased the rate of 5-hydroxytryptophan accumulation after NSD 1015, the rate of serotonin decline after α-propyldopacetamide, and the rate of 5-hydroxyindoleacetic acid accumulation after probenecid. The elevation of serotonin was probably due to weak inhibition of monoamine oxidase. Quipazine reversibly inhibited the oxidation of serotonin by rat brain monoamine oxidase and protected against the irreversible inactivation of the enzyme . Quipazine also was a potent inhibitor of serotonin uptake into brain synaptosomes and attained concentrations in brain higher than the IC50. However, quipazine did not prevent the depletion of brain serotonin by p-chloroamphetamine . In addition to stimulating serotonin receptors in brain, quipazine may inhibit monoamine oxidase and serotonin reuptake . 相似文献
20.
Synthesis of diphtheria toxin in E. coli cell-free lysate 总被引:7,自引:0,他引:7
An cell-free lysate was used to translate RNA from nontoxinogenic C7(?), C7 infected with β tox+ corynebacteriophage, and strain PW8. De novo synthesis of toxin was detected by immune precipitation with antitoxin, ADP-ribosylation of mammalian elongation factor 2 and rabbit skin test. The results indicated that toxin is produced in the protein synthesizing system primed with RNA from cells infected with tox+ bacteriophage and is absent in systems primed with RNA from C7(?) cells. 相似文献