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31.
Summary Voltage-clamped single nerve fibers of the frogRana esculenta were treated with the carboxyl group activating reagent N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in the presence of different primary amines and without added amine. Carboxyl groups form stable amide bonds with primary amines in the presence of EEDQ. EEDQ treatment reduced the sodium current considerably and irreversibly, regardless of the presence of a primary amine in the Ringer's solution. The potassium current was also reduced. After modification the reduced sodium currents inactivated slowly and incompletely. The descending branch of the sodium current-voltage relation,I
Na(E), was shifted along the voltage axis in the depolarizing direction. The size of the shift was strongly dependent on the amine present during modification with EEDQ. The voltage-dependence of sodium inactivation,h
x
(E), was shifted to more positive values of membrane potential by EEDQ in the presence of ethylenediamine (11 mV) and glucosamine (3 mV). In contrast, a small shift to more negative potentials occurred in the presence of taurine (–3 mV) or without the addition of an amine (–2 mV). A tenfold increase of the calcium concentration still shifted theI
Na(E) andh
x
(E) curves of the chemically modified fibers. However, these shifts were smaller than those observed on untreated fibers. The currents remaining after the modification were completely blocked by tetrodotoxin; no change of the reversal potential occurred. 相似文献
32.
Dipple Anthony Pigott Margaret A. Milner John A. 《Biological trace element research》1986,10(2):153-157
Since selenium has been found to exert a protective action against carcinogenesis in various systems, the mechanism where-by
sodium selenite inhibits DNA binding of the carcinogen, 7,12-dimethylbenz[a]anthracene, was investigated. It was found that
selenite preferentially reduced DNA binding occurring through ananti-dihydrodiol epoxide metabolite of this carcinogen by inhibiting the induction of an enzyme system that generates this specific
reactive metabolite. 相似文献
33.
Bernhard Kadenbach 《Journal of bioenergetics and biomembranes》1986,18(1):39-54
The present view on the regulation of respiration and ATP synthesis in higher organisms implies only Michaelis-Menten type kinetics and respiratory control as regulatory principles. Recent experimental observations, suggesting further regulatory mechanisms at respiratory chain complexes, are reviewed. A new hypothesis is presented implying regulation of respiration and ATP synthesis in higher organisms mainly via allosteric modification of respiratory chain complexes, in particular of cytochromec oxidase. The allosteric effectors, e.g., metabolites, cofactors, ions, hormones, and the membrane potential are suggested to change the activity and the coupling degree of cytochromec oxidase by binding to specific sites at nuclear coded subunits. Recent results on the structure and activity of cytochromec oxidase, supporting the hypothesis, are reviewed.Dedicated to Professor Dr. Carl Martius on the occasion of his 80th birthday. 相似文献
34.
It was shown that tRNA fromAzotobacter vinelandii grown in the presence of ammonium chloride lacks ribothymidine while that grown in the absence of the ammonium salt contains
this modified nucleoside. [32P]-Labelled tRNA from this organism grown in a medium containing the ammonium salt was digested with RNase T1 and the pseudouridinecontaining
tetranucleotide, common to all tRNAs was isolated and analysed for the nucleoside replacing the ribothymidine. It was found
to be uridine. Cells previously labelled with [32P]-phosphate in the ammonium salt medium were washed and incubated in the ammonium saltfree medium to test whether ribothymidine
would be formed upon removal of the ammonium ions. Methylation of the uridine did not take place. 相似文献
35.
The structural organization of Tetrahymena pyriformis is such that its cilia are remote from the main centers of lipid metabolism. As a result, the ciliary membrane lipid composition of cells exposed to low-temperature stress is initially unaffected by the significant metabolic changes induced in microsomal membranes. Nevertheless, changes in the ciliary membrane lipid composition can be detected during the first 4 h of cold exposure. A combination of in vivo and in vitro experiments has provided strong evidence for a substantial retailoring of ciliary phospholipid molecular species in situ in the absence of any importation of lipids from the cell interior or change in overall ciliary fatty acid composition. The mechanism responsible for the ciliary lipid changes is independent of the one(s) triggering internal acclimation responses. Our observations establish for the first time that chilling stress can simultaneously induce separate and distinctive lipid modification responses in different parts of a cell. This finding could be important in identifying the molecular ‘sensor’ capable of actuating stress-induced lipid changes. 相似文献
36.
A comparison of specific antibodies induced by unfolded actins modified either by oxidation or by arylation of lysine residues was reported. We have focused our work on binding properties with filamentous actin and located its preferential antigenic sites for the anti-arylated-actin antibodies in the C-part of the molecule. An interference of anti-oxidized actin antibodies upon actin polymerisation has also been reported. 相似文献
37.
Chemical modification of Rhodospirillum rubrum chromatophores by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) results in inactivation of photophosphorylation, Mg2+-ATPase, oxidative phosphorylation and ATP-driven transhydrogenase, with apparent first-order kinetics. Other energy-linked reactions such as light-driven transhydrogenase and light-dependent proton uptake were insensitive to NBD-Cl. The Ca2+-ATPase activity of the soluble coupling factor from chromatophores (R. rubrum F1) was inactivated by NBD-Cl with kinetics resembling those described for Mg2+-ATPase and photophosphorylation activities of chromatophores. Both NBD-chromatophores and NBD-R. rubrum F1 fully recovered their activities when subjected to thiolysis by dithioerythritol. Phosphoryl transfer reactions of chromatophores and Ca2+-ATPase activity of R. rubrum F1 were fully protected by 5 mM Pi against modification by NBD-Cl. ADP or ATP afforded partial protection. Analysis of the protection of Ca2+-ATPase activity by Pi indicated that NBD-Cl and Pi are mutually exclusive ligands. Spectroscopic studies revealed that tyrosine and sulfhydryl residues in R. rubrum F1 underwent modification by NBD-Cl. However, the inactivation was only related to the modification of tyrosine groups. 相似文献
38.
Xin-Min Cao Lan-Hsiang Huang Chris M. Farnet Melanie Ehrlich 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(2):237-243
After digestion by TaqI or nicking by DNAase I, five highly modified bacteriophage DNAs were tested as substrates for T4 DNA ligase. The DNAs used were from phages T4, XP12, PBS1, SP82, and SP15, which contain as a major base either glucosylated 5-hydroxymethylcytosine, 5-methylcytosine, uracil, 5-hydroxymethyluracil, or phosphoglucuronated, glucosylated 5-(4′,5′-dihydroxypentyl)uracil, respectively. The relative ability of cohesive-ended TaqI fragments of these DNAs and of normal, λ DNA to be ligated was as follows: . TaqI-T4 DNA fragments were also inefficiently ligated by Escherichia coli DNA ligase. However, annealing-independent ligation of DNAase I-nicked T4, PBS1, and λ DNAs was equally efficient. We conclude that the poor ligation of TaqI fragments of T4 and PBS1 DNAs was due to the hydroxymethylation (and glucosylation) of cytosine residues at T4's cohesive ends and the substitution of uracil residues for thymine residues adjacent to PBS1's cohesive ends destabilizing the annealing of the restriction fragments. Only SP15 DNA with its negatively charged, modified base was unable to serve as a substrate for T4 DNA ligase in an annealing-independent reaction; therefore, its modification directly interfered with enzyme binding or catalysis. 相似文献
39.
Summary We have investigated the ion permeability properties of sodium channels purified from eel electroplax and reconstituted into liposomes. Under the influence of a depolarizing diffusion potential, these channels appear capable of occasional spontaneous openings. Fluxes which result from these openings are sodium selective and blocked (from opposite sides of the membrane) by tetrodotoxin (TTX) and moderate concentrations of the lidocaine analogue QX-314. Low concentrations of QX-314 paradoxically enhance this channel-mediated flux. N-bromoacetamide (NBA) and N-bromosuccinimide (NBS), reagents which remove inactivation gating in physiological preparations, transiently stimulate the sodium permeability of inside-out facing channels to high levels. The rise and subsequent fall of permeability appear to result from consecutive covalent modifications of the protein. Titration of the protein with the more reactive NBS can be used to produce stable, chronically active forms of the protein. Low concentrations of QX-314 produce a net facilitation of channel activation by NBA, while higher concentrations produce block of conductance. This suggests that rates of modifications by NBA which lead to the activation of permeability are influenced by conformational changes induced by QX-314 binding. 相似文献
40.
Structural gene isolation and prepeptide sequence of gallidermin, a new lanthionine containing antibiotic 总被引:18,自引:0,他引:18
Norbert Schnell Karl-Dieter Entian Friedrich Götz Thomas Hörner Roland Kellner Günther Jung 《FEMS microbiology letters》1989,58(2-3):263-267
Peptide antibiotics containing lanthionine and 3-methyllanthionine bridges, named lantibiotics are of increasing interest. A new lantibiotic, gallidermin, has been isolated from Staphyloccus gallinarum. Here we report the isolation of its structural gene which we name gdmA. In all lantibiotics so far studied genetically, three peptides can be formally distinguished: (i) the primary translation product, which we call the prepeptide; (ii) the propeptide lacking the leader sequence and (iii) the mature lantibiotic. Unlike the plasmid-coded epidermin, gdmA is located on the chromosome. The gdmA locus codes for a 52 amino acid residue prepeptide, consisting of an alpha-helical leader sequence of hydrophilic character, which is separated from the C-terminus (propeptide) by a characteristic proteolytic processing site (Pro-2 Arg-1 Ile1). Although pro-gallidermin differs from pro-epidermin (a recently isolated lantibiotic) only by a single amino acid residue exchange. Leu instead of Ile, the N-terminus of the prepeptide differs by an additional two exchanges. 相似文献