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91.
Methanogenesis in thermophilic biogas reactors 总被引:2,自引:0,他引:2
Birgitte Kiær Ahring 《Antonie van Leeuwenhoek》1995,67(1):91-102
Methanogenesis in thermophilic biogas reactors fed with different wastes is examined. The specific methanogenic activity with acetate or hydrogen as substrate reflected the organic loading of the specific reactor examined. Increasing the loading of thermophilic reactors stabilized the process as indicated by a lower concentration of volatile fatty acids in the effluent from the reactors. The specific methanogenic activity in a thermophilic pilot-plant biogas reactor fed with a mixture of cow and pig manure reflected the stability of the reactor. The numbers of methanogens counted by the most probable number (MPN) technique with acetate or hydrogen as substrate were further found to vary depending on the loading rate and the stability of the reactor. The numbers of methanogens counted with antibody probes in one of the reactor samples was 10 times lower for the hydrogen-utilizing methanogens compared to the counts using the MPN technique, indicating that other non-reacting methanogens were present. Methanogens that reacted with the probe againstMethanobacterium thermoautotrophicum were the most numerous in this reactor. For the acetate-utilizing methanogens, the numbers counted with the antibody probes were more than a factor of 10 higher than the numbers found by MPN. The majority of acetate utilizing methanogens in the reactor wereMethanosarcina spp. single cells, which is a difficult form of the organism to cultivatein vitro. No reactions were observed with antibody probes raised againstMethanothrix soehngenii orMethanothrix CALS-1 in any of the thermophilic biogas reactors examined. Studies using 2-14C-labeled acetate showed that at high concentrations (more than approx. 1 mM) acetate was metabolized via the aceticlastic pathway, transforming the methyl-group of acetate into methane. When the concentration of acetate was less than approx. 1 mM, most of the acetate was oxidized via a two-step mechanism (syntrophic acetate oxidation) involving one organism oxidizing acetate into hydrogen and carbon dioxide and a hydrogen-utilizing methanogen forming the products of the first microorganism into methane. In thermophilic biogas reactors, acetate oxidizing cultures occupied the niche ofMethanothrix species, aceticlastic methanogens which dominate at low acetate concentrations in mesophilic systems. Normally, thermophilic biogas reactors are operated at temperatures from 52 to 56° C. Experiments using biogas reactors fed with cow manure showed that the same biogas yield found at 55° C could be obtained at 61° C after a long adaptation period. However, propionate degradation was inhibited by increasing the temperature. 相似文献
92.
Susanne J. Andersen 《Antonie van Leeuwenhoek》1995,68(2):165-171
A large number ofPenicillium nalgiovense isolates from mould fermented sausages and the ex type culture were examined for characters of morphology, physiology and production of secondary metabolites. To separate biotypes within theP. nalgiovense species, the data obtained were evaluated using multivariate statistical methods. The macromorphological characters of the ex type culture and isolates from meat products appeared to be distinctive. The ex type culture is characterized by a brown reverse on both Czapek yeast extract and malt extract agar while the isolates from meat products have a yellow to orange reverse. Proteolytic and/or lipolytic activity was demonstrated by 75% of the examined cultures and all of them demonstrated ability to utilize lactate as sole carbon source. Growth on creatine sucrose agar was very inhibited and acid production was absent or very weak. TLC analysis showed production of three unknown secondary metabolites that constituted the characteristic profile. HPLC analysis showed production of only three known secondary metabolites; chrysogine (96%), nalgiolaxin and nalgiovensin (9%). The ex type culture produced nalgiolaxin and nalgiovensin but not chrysogine. The chemometric evaluation showed thatP. nalgiovense isolates from meat products from a homogenous species, which can not be divided into biotypes. The only indication of grouping, beside a separation of the ex type culture, was related to the conidium colour (white, turquoise or grey green). The examinedP. nalgiovense isolates showed some resemblance (morphologically and chemically) toP. chrysogenum. 相似文献
93.
94.
95.
The concentration of VIP was measured radioimmunochemically in cerebrospinal fluid (CSF) from 14 healthy volunteers and from 22 patients with multiple sclerosis. Significantly lower levels of VIP was obtained in the patients (18 +/- 3 pmol/l) than in controls (37 +/- 4 pmol/l). There was no correlation between the level of VIP in CSF and other CSF parameters such as albumin. IgG or cell content; nor between VIP concentration and the physical handicap or neuropsychiatric symptoms. There was a trend towards lower values of VIP in patients with steadily progressing rather than intermittent course of the disease but the difference between the groups was not significant. 相似文献
96.
Sara S. Tynan Niels H. Andersen Max T. Wills Laurence A. Harker Stephen R. Hanson 《Prostaglandins & other lipid mediators》1984,27(5):683-696
The ω-chain variant analogs of prostacyclin (PGI2) and PGD2 in which the n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1)(1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI2, but converts PGD2 to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD2 by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD2, cyclohexyl-PGD2, and BW-245C; with essentially no effect on PGI2, cyclohexyl-PGI2 and PGE2 at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre (2,3), but supports the view that the anti-aggregatory effect of high doses of PGE2 () is mediated by the PGI2 receptor (4). The hydantoin acts at the platelet PGD2 receptor. 相似文献
97.
Platelet-derived growth factor stimulates chemotaxis and nucleic acid synthesis in the protozoan Tetrahymena 总被引:2,自引:0,他引:2
Platelet-derived growth factor (PDGF) is in concentrations of a few nanograms per ml a very active chemoattractant for the free-living ciliated protozoan Tetrahymena; at the same time it induces a rapid increase in incorporation of radioactive nucleic acid precursors into RNA and DNA. We find it remarkable that this lower eukaryote responds to platelet-derived growth factor in very much the same way as fibroblastic cells. 相似文献
98.
Yeast RNA polymerase III. Chromatographic, catalytic and DNA-binding properties are highly dependent on the type of anion 总被引:4,自引:0,他引:4
The chromatographic, catalytic and DNA-binding properties of yeast RNA polymerase III are highly affected by both concentration and type of salt. The type of anion is an especially important modulating factor for the enzymological properties of the enzyme. When acetate or sulfate anions are substituted for chloride anions, RNA polymerase III exhibits a higher affinity for DEAE-Sephadex A25, becomes able to transcribe DNA at relatively high ionic strength and shows a significant increase in the binding strength to DNA. A quantitative analysis of the binding of the enzyme to single-stranded DNA shows that the number of ionic contacts in the complex is not affected by the type of anion, but the nonionic contribution to the binding constant is significantly increased when acetate is substituted for chloride. 相似文献
99.
Birgitte Munch-Petersen 《Molecular and cellular biochemistry》1984,64(2):173-185
Summary The two thymidine kinases, TK 1 and TK 2, found in phytohemagglutinin-stimulated human lymphocytes and the thymidine kinase, TK 2N, found in unstimulated human lymphocytes were purified and characterized. All three kinases had molecular weights between 70000 and 75000 which increased to 170000–200000 in the presence of 2 mM ATP.Studies on the kinetic properties of the enzymes with thymidine and ATP as the substrates and dTTP as the inhibitor showed clear differences between TK 1 and TK 2, but a close similarity between TK 2 and TK 2N. With thymidine as the variable substrate, TK 1 showed Michaelis-Menten kinetics, whereas TK 2 and TK 2N showed characteristic biphasic kinetics. With ATP as the variable substrate, all three enzymes showed positive cooperative kinetics, but TK 2 and TK 2N lost the cooperativity in the presence of dTTP. The results from inhibition studies showed, that dTTP was a cooperative inhibitor of TK 1 but a non-cooperative inhibitor of TK 2 and TK 2N. 相似文献
100.
Partial purification, characterization and translation in vitro of rat liver metallothionein messenger ribonucleic acid. 总被引:8,自引:1,他引:7
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Poly(A)+ (polyadenylated) mRNA coding for metallothioneins was purified 13-fold from rat liver polyribosomes and was identified by its ability to direct the biosynthesis of these proteins in a wheat-germ cell-free system. The carboxymethylated products of the protein-synthesizing system in vitro were analysed with sodium dodecyl sulphate/20% polyacrylamide-gel electrophoresis. The labelled compounds [3H]serine and [35S]cysteine were incorporated at high specific radioactivity into proteins that co-migrated with authentic metallothioneins. No [3H]leucine incorporation was found, in agreement with the amino acid composition of the metallothioneins. Metallothionein mRNA had a sedimentation coefficient of 9 S and carried a maximum of four ribosomes. At 5 h after a subcutaneous injection of ZnCl2 or CdCl2 (10 mumol/kg body wt.), the amount of this mRNA increased approx. 2- and 4-fold respectively, on the basis of translation in vitro. The increase in metallothionein mRNA (defined by translation in the wheat-germ system) was transient and, after CdCl2 treatment, fell back to control values by 17 h. Metallothioneins constituted a maximum of 0.8% of the total protein products synthesized in the wheat-germ system by total mRNA isolated from rat liver after CdCl2 treatment. 相似文献