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101.
From anaerobic freshwater enrichment cultures with 3-hydroxybenzoate as sole substrate, a slightly curved rod-shaped bacterium was isolated in coculture with Desulfovibrio vulgaris as hydrogen scavenger. The new isolate degraded only 3-hydroxybenzoate or benzoate, and depended on syntrophic cooperation with a hydrogenoxidizing methanogen or sulfate reducer. 3-Hydroxybenzoate was degraded via reductive dehydroxylation to benzoate. With 2-hydroxybenzoate (salicylate), short coccoid rods were enriched from anaerobic freshwater mud samples, and were isolated in defined coculture with D. vulgaris. This isolate also fermented 3-hydroxybenzoate or benzoate in obligate syntrophy with a hydrogen-oxidizing anaerobe. The new isolates were both Gram-negative, non-sporeforming strict anaerobes. They fermented hydroxybenzoate or benzoate to acetate, CO2, and, presumably, hydrogen which was oxidized by the syntrophic partner organism. With hydroxybenzoates, but not with benzoate, Acetobacterium woodii could also serve as syntrophic partner. Other substrates such as sugars, alcohols, fatty or amino acids were not fermented. External electron acceptors such as sulfate, sulfite, nitrate, or fumarate were not reduced. In enrichment cultures with 4-hydroxybenzoate, decarboxylation to phenol was the initial step in degradation which finally led to acetate, methane and CO2. 相似文献
102.
Sea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H2O2) prevents polyspermy in Arbacia punctulata. We found that it is not H2O2 but probably hypochlorous acid/hypochlorite (HOCl/OCl?) derived from H2O2 that is toxic to the supernumerary sperm. The spermicidal activity of H2O2 is potentiated by at least one order of magnitude by cupric ions (Cu2+). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu2+. More-over, substitution of Cu2+ by ferrous ions (Fe2+), which are known to cause formation of ·OH from H2O2, had no effect on fertilization even at 102?103 times higher concentrations. In contrast, 3-amino-1,2,4-triazole (AT), an HOCl/OCl? scavenger, totally reversed the toxic effects of Cu2+. Furthermore, we found that HOCl/OCl? is generated in solutions of H2O2 and Cu2+ in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl?. HOCl/OCl? generated by Cu2+ from H2O2 and Cl?, a low concentration of exogenously added HOCl/OCl?, or increased concentrations of H2O2 has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl? from the Cl? present in sea water through reaction with H2O2 generated by the newly fertilized egg. 相似文献
103.
J L Markley D H Croll R Krishnamoorthi G Ortiz-Polo W M Westler W C Bogard M Laskowski 《Journal of cellular biochemistry》1986,30(4):291-309
The traditional approach of using homologous sequences to elucidate the role of specific amino acid residues in protein structure and function becomes more meaningful as the number of differences is minimized, with the limit being alteration of a single residue. For small proteins in solution, NMR spectroscopy offers a means of obtaining detailed information about each residue and its response to a given change in the protein sequence. Extraction of this information has been aided by recent progress in spectrometer technology (higher magnetic fields, more sensitive signal detection, more sophisticated computers) and experimental strategies (new NMR pulse sequences including multiple-quantum and two-dimensional NMR methods). The set of avian ovomucoid third domains, which consists of the third domain proper plus a short leader (connecting peptide) and has a maximum of 56 amino acid residues, offers an attractive system for developing experimental methods for investigating sequence-structure and structure-function relationships in proteins. Our NMR results provide examples of sequence effects on pKa' values, average conformation, and internal motion of amino acid side chains. 相似文献
104.
Rudolph Pipa 《Archives of insect biochemistry and physiology》1986,3(5):471-483
Unilateral section of the nervi corporis allati I (NCA-1) of isolated, starved, adult, virgin Periplaneta americana disinhibited oocyte growth during a specific period following their adult emergence. The effect required that the corpus allatum (CA) be free of NCA-1 innervation for 4 days beyond the time the females were 7–8 days old. The onset of this sensitive period corresponds to when most isolated, starved virgins become sexually receptive. The results suggest that NCA-1 inhibition of CA activity, initiated about 7 days, is relieved by mating. When done on sexually receptive, starved virgins, unilateral NCA-1 section was as effective as insemination for stimulating growth and chorionation of the first generation of oocytes. Neural inhibition of juvenile hormone (JH) secretion by the CA may also explain diminished production of oocytes by isolated, fed virgins, for during 30 days following unilateral NCA-1 section they produced 2.6 to 5 times more oothecae than did controls with a single CA removed or after the sham operation. The number of oothecae deposited by fed virgins was similarly increased after bilateral NCA-1 section, but to a lesser extent than when the operation was done on fed, inseminated females of the same age. Specificity of the response of the CA to denervation was substantiated by experiments in which the CA were extirpated and reimplanted, by topically applying C16JH, and by experiments in which the nervus corporis cardiaci 1 and 2 on the right or left side were severed. 相似文献
105.
Protein folding kinetics by combined use of rapid mixing techniques and NMR observation of individual amide protons 总被引:9,自引:0,他引:9
A method to be used for experimental studies of protein folding introduced by Schmid and Baldwin (J. Mol. Biol. 135: 199-215, 1979), which is based on the competition between amide hydrogen exchange and protein refolding, was extended by using rapid mixing techniques and 1H NMR to provide site-resolved kinetic information on the early phases of protein structure acquisition. In this method, a protonated solution of the unfolded protein is rapidly mixed with a deuterated buffer solution at conditions assuring protein refolding in the mixture. This simultaneously initiates the exchange of unprotected amide protons with solvent deuterium and the refolding of protein segments which can protect amide groups from further exchange. After variable reaction times the amide proton exchange is quenched while folding to the native form continues to completion. By using 1H NMR, the extent of exchange at individual amide sites is then measured in the refolded protein. Competition experiments at variable reaction times or variable pH indicate the time at which each amide group is protected in the refolding process. This technique was applied to the basic pancreatic trypsin inhibitor, for which sequence-specific assignments of the amide proton NMR lines had previously been obtained. For eight individual amide protons located in the beta-sheet and the C-terminal alpha-helix of this protein, apparent refolding rates in the range from 15 s-1 to 60 s-1 were observed. These rates are on the time scale of the fast folding phase observed with optical probes. 相似文献
106.
A general method for the synthesis of azido-ubiquinone derivatives has been developed directly by substituting one hydrogen atom on the benzoquinone ring with an azido group under weakly acidic conditions. The reaction takes several hours and the yield is generally low. The azido-ubiquinone was purified by preparative thin layer chromatography, and identified by NMR, IR and mass spectra. All the synthesized azido-ubiquinone derivatives show partial activity in mediating biological electron transfer in the dark, and show partial or complete inhibition upon photolysis. 相似文献
107.
A chemiluminescent method for measuring the concentration of activated oxygen species (O22 and H2O2) is described. Its main features are: high sensitivity (10?9 M H2O2), its applicability to systems with high optical absorbance in the visible spectral region, a wide linear dynamic range, and the possibility for recording the kinetics of the processes, in which activated oxygen species are involved. 相似文献
108.
Maureane Hoffman Steven R. Feldman Salvatore V. Pizzo 《Biochimica et Biophysica Acta (BBA)/General Subjects》1983,760(3):421-423
Mouse peritoneal macrophages activated by bacillus Calmette-Guerin (BCG) were incubated with human α2-macroglobulin converted to its ‘fast’ form with either trypsin or methylamine before being stimulated with phorbol myrystate acetate. Both α2-macroglobulin-trypsin and α2-macroglobulin-methylamine inhibited macrophage production of superoxide anion (O2−) while native α2-macroglobulin had little effect except at high concentration. The α2-macroglobulin ‘fast’ forms, which bind with a Kd of about 8 nM, inhibited 50% generation of O2−(ID50) at a concentration of 7 nM while α2-macroglobulin inhibited O2− production with an ID50 of 141 nM. The ‘fast’ forms of α2-macroglobulin may play a role in the feedback regulation of inflammatory reactions. 相似文献
109.
Giorgio Brandi Flaminio Cattabeni Amedeo Albano Orazio Cantoni 《Free radical research》1989,6(1):47-55
Escherichia coli lethality by hydrogen peroxide is characterized by two modes of killing. In this paper we have found that hydroxyl radicals (OH -) generated by H2O2 and intracellular divalent iron are not involved in the induction of mode one lethality (i.e. cell killing produced by concentrations of H2O2 lower than 2.5 mM). In fact, the OH radical scavengers, thiourea, ethanol and dimethyl sulfoxide, and the iron chelator, desferrioxarnine, did not affect the survival of cells exposed to 2.5mM H2O2. In addition cell vulnerability to the same H2O2 concentration was independent on the intracellular iron content. In contrast, mode two lethality (i.e. cell killing generated by concentrations of H2O2 higher than 10mM) was markedly reduced by OH radical scavengers and desferrioxamine and was augmented by increasing the intracellular iron content.
It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide. 相似文献
It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide. 相似文献
110.
Saroj Sanan Geeta Sharma Rakesh Malhotra Devindar P. Sanan Parveen Jain Prem Vadhera 《Free radical research》1989,6(1):29-38
Haemorrhagic shock was produced in anaesthetized dogs, by rapid arterial bleeding to mean arterial blood pressure 35 mmHg, and maintained oligaemic for 4 h followed by return of withdrawn blood(R0WB). Dogs were observed for 72 h after ROWB for survival and recovery, and, for histopathological (HP) studies on liver, dogs were sacrificed 2 h after ROWB in non-survival experiments. Desferrioxamine mesylate (25mg/kg) was administered intra-muscularly at 2,3 and 4h after blood loss in survival experiments and for HP studies the drug was given at 4 h in one group and at 2 h plus 4 h after blood loss in the second group. With the drug given at 3 or 4h, survival was 70% and 100% while in the 2h and the untreated groups it was 50%. Recovery was rapid in all the drug treated survivors, few became conscious within 30min. showed slight activity by 4-6 h, all were almost normally active by 24 and fully so by 72 h after ROWB. All the 5 control survivors remained unconscious/drowsy upto 24 h; 3 were sluggish at 72 h. By group analysis, serum iron elevation during the oligaemic and at the end of the post-oligaemic phase was less in the drug-treated animals. HP changes of shock in the liver studied by light microscopy, were markedly reduced in severity and were less prevalent in the drug-treated dogs. The salutory effects of desferrioxamine may be due to inhibition of iron catalyzed free-radical production and tissue damage, through its strong iron chelating action. It may have a therapeutic advantage in this emergency condition without the disadvantages of toxicity inherent in prolonged use. 相似文献