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11.
H. Okuyama Akio Ueno Daisuke Enari Naoki Morita Teruo Kusano 《Archives of microbiology》1997,169(1):29-35
A 9-hexadecenoic acid cis-trans isomerase (9-isomerase) that catalyzed the cis-to-trans isomerization of the double bond of free 9-cis-hexadecenoic acid [16:1(9c)] was purified to homogeneity from an extract of Pseudomonas sp. strain E-3 and characterized. Electrophoresis of the purified enzyme on both incompletely denaturing and denaturing polyacrylamide
gels yielded a single band of a protein with a molecular mass of 80 kDa, suggesting that the isomerase is a monomeric protein
of 80 kDa. The 9-isomerase, assayed with 16:1(9c) as a substrate, had a specific activity of 22.8 μmol h–1 (mg protein)–1 and a K
m of 117.6 mM. The optimal pH and temperature for catalysis were approximately pH 7–8 and 30° C, respectively. The 9-isomerase
catalyzed the cis-to-trans conversion of a double bond at positions 9, 10, or 11, but not that of a double bond at position 6 or 7 of cis-mono-unsaturated fatty acids with carbon chain lengths of 14, 15, 16, and 17. Octadecenoic acids with a double bond at position
9 or 11 were not susceptible to isomerization. These results suggest that 9-isomerase has a strict specificity for both the
position of the double bond and the chain length of the fatty acid. The enzyme catalyzed the cis-to-trans isomerization of fatty acids in a free form, and in the presence of a membrane fraction it was also able to isomerize 16:1(9c)
esterified to phosphatidylethanolamine. The 9-isomerase was strongly inhibited by catecholic antioxidants such as α-tocopherol
and nordihydroguaiaretic acid, but was not inhibited by 1,10-phenanthroline or EDTA or under anoxic conditions. Based on these
results, the possible mechanism of catalysis by this enzyme is discussed.
Received: 21 May 1997 / Accepted: 5 September 1997 相似文献
12.
Rosa Margesin 《Extremophiles : life under extreme conditions》2009,13(2):257-262
Three bacterial (Pedobacter heparinus, Pedobacter piscium, Pedobacter cryoconitis) and three yeast strains (Saccharomyces cerevisiae, Leucosporidiella creatinivora, Rhodotorula glacialis) of different thermal classes (mesophiles and psychrophiles) were tested for the effect of temperature on a range of growth
parameters, including optical density, viable cell numbers, and cell dry mass, in order to determine the temperature conditions
under which maximum biomass formation is obtained. Maximum values of growth parameters obtained at the stationary growth phase
of the strains were used for statistical calculation. Temperature had a significant (P ≤ 0.05) effect on all growth parameters for each strain; correlations between the growth parameters were significant (P ≤ 0.05–0.01). The maximum growth temperature or the temperature at which microbial growth was fastest was in no case the temperature
at which the investigated strains produced the highest amount of biomass. All tested psychrophilic bacteria and yeast strains
produced highest amounts of cells (as calculated per mg cell dry mass or per OD600 unit) at 1°C, while cell numbers of mesophiles were highest at 20°C. Thus, cultivation temperatures close to the maximum
growth temperature are not appropriate for studying psychrophiles. 相似文献
13.
Two structurally different monomeric and dimeric types of isocitrate dehydrogenase (IDH; EC 1.1.1.42) isozymes were confirmed to exist in a psychrophilic bacterium, Colwellia psychrerythraea, by Western blot analysis and the genes encoding them were cloned and sequenced. Open reading frames of the genes (icd-M and icd-D) encoding the monomeric and dimeric IDHs of this bacterium, IDH-M and IDH-D, were 2,232 and 1,251 bp in length and corresponded to polypeptides composed of 743 and 416 amino acids, respectively. The deduced amino acid sequences of the IDH-M and IDH-D showed high homology with those of monomeric and dimeric IDHs from other bacteria, respectively. Although the two genes were located in tandem, icd-M then icd-D, on the chromosomal DNA, a Northern blot analysis and primer extension experiment revealed that they are transcribed independent of each other. The expression of the monomeric and dimeric IDH isozyme genes in C. maris, a psychrophilic bacterium of the same genus as C. psychrerythraea, is known to be induced by low temperature and acetate, respectively, but no such induction in the expression of the C. psychrerythraea icd-M and icd-D genes was detected. IDH-M and IDH-D overexpressed in Escherichia coli were purified and characterized. In C. psychrerythraea, the IDH-M isozyme is cold-active whereas IDH-D is mesophilic, which is similar to C. maris that contains both cold-adapted and mesophilic isozymes of IDH. Experiments with chimeric enzymes between the cold-adapted monomeric IDHs of C. psychrerythraea and C. maris (IDH-M and ICD-II, respectively) suggested that the C-terminal region of the C. maris IDH-II is involved in its catalytic activity. 相似文献
14.
Recently, a unique archaeal/bacterial community that grows in a macroscopically visible string-of-pearls-like structure in cold (~10 °C), sulfurous marsh water was discovered. Here, a new technique is described that allows the fast and reliable growth of these string-of-pearls-like microbial communities in larger quantities on polyethylene nets in nature. The microbial net population, estimated to consist of about 10,000 single pearls, can be harvested once a week and the archaeal cells selectively separated by density gradient centrifugation. As in native pearls, the archaeal cell fraction obtained consisted of a single type of coccoid cells only, 0.6 µm in diameter. This novel type of euryarchaea has been tentatively named SM1 euryarchaeon. Electron microscopy and immuno-fluorescence in situ hybridization (immuno-FISH) revealed that about 100 pili-like fibers, up to 3 µm in length, emanate radially from the surface of each cell. The SM1 euryarchaeal cells exhibited a viability of about 90%. The optimal conditions for viability were temperatures between –2 °C and 20 °C, pH 5–9, and low salt conditions; cell viability was independent of oxygen partial pressures. The cultures stained gram-positive, the cell wall was sensitive to SDS, EDTA and Proteinase K treatment. The cells did not exhibit the typical fluorescence for methanogens and did not contain coenzyme F420. The G+C-content was 34.5 mol%. 相似文献
15.
Escherichia coli and later found to be a cold-shock response common to many bacterial species. CspA of 7.4 kD, a major cold-shock protein
in E. coli, has been shown to share structural similarity with a class of eukaryotic Y box proteins which have RNA-binding domains.
Transient synthesis of CspA upon cold shock is mediated by increased stabilization of the mRNA at low temperatures. The proposed
role of some cold-shock proteins including CspA in the bacterial adaptation to low temperatures is to function as a RNA chaperone
in the regulation of translation. Some enzymes of psychrotrophic or psychrophilic bacteria exhibit unique features of a cold-adapted
enzyme, high catalytic activity at a low temperature and rapid inactivation at a moderate temperature. A monomeric isocitrate
dehydrogenase isozyme (IDH-II) of a psychrophilic bacterium, Vibrio sp. strain ABE-1, is a typical cold-adapted enzyme. In addition, this enzyme is induced at low temperatures. Low temperature-dependent
expression of icdll encoding IDH-II is controlled by two different cis-elements located at the untranslated upstream region of the gene, one is a silencer and the other is essential for the low
temperature response. The physiological role of IDH-II is evaluated by transforming E. coli with icdll. The growth rate of the E. coli transformants at low temperatures is dependent on the level of expressed IDH-II activity.
Received 11 January 1999/ Accepted in revised form 6 April 1999 相似文献
16.
The gene encoding a heat-labile uracil-DNA glycosylase (UDG) from a psychrophilic, gram-positive marine strain (BMTU3346)
has been cloned, sequenced, and expressed in Escherichia coli. The UDG is a cold-active enzyme with an apparent temperature optimum of 35°C and a half-life of 2 min at 40°C. The amino
acid sequence shows an identity of 39.1%–46.2% to UDGs from mesophilic bacteria. The primary structure was examined for features
that could be related to the thermolability of the enzyme. The amino acid sequence of the heat-labile UDG shows 22 differences
with respect to the consensus sequence derived from bacterial UDGs. Features previously recognized in cold-active enzymes
such as extended surface loops or a decrease in the number of arginine residues or proline residues in loops were not observed.
Because dominant features that could be related to the thermolability of the UDG from BMTU3346 cannot be identified, more
subtle modifications of the conformation seem to be responsible for its thermolability.
Received: June 30, 1999 / Accepted: November 12, 1999 相似文献
17.
18.
Jahandideh S Abdolmaleki P Jahandideh M Barzegari Asadabadi E 《Journal of theoretical biology》2007,246(1):159-166
A systematic analysis compared sequence and structural parameters distributions between 13 pairs of psychrophilic and mesophilic proteins for elucidating the cold adaptation parameters. The results of statistical test (t-test) revealed that helical content, tight turn content, disulfide bonds and hydrogen bonds do not show significant difference between psychrophilic and mesophilic proteins. However, it was demonstrated in this study that a larger proportion of open beta-turn in psychrophilic proteins is an effective parameter in specific activity at low temperature. In addition, substitution of amino acids of charged and aliphatic groups with amino acids of tiny and small groups in protein chains, tight turns and alpha-helices in the direction from mesophilic to psychrophilic proteins is one of the mechanisms of low temperature adaptation. Such sequence and structural parameter differences would help to develop a strategy for designing cold-adapted proteins. 相似文献
19.
The methanogenic community structures of six anaerobic sludges were examined using culture-independent techniques. The sludges were obtained from full-scale and laboratory-scale bioreactors, treating a variety of low- and high-strength, simple and complex wastewaters at psychrophilic (10-14 degrees C), mesophilic (37 degrees C) and thermophilic (55 degrees C) temperatures. Amplified rDNA restriction analysis identified 18 methanogenic operational taxonomic units in the six samples. 16S rRNA gene sequencing and phylogenetic reconstruction demonstrated that five separate groups of methanogens were represented with Methanosaeta-like species dominant in all sludges, but particularly in samples from a psychrophilic bioreactor treating low-strength synthetic sewage (75% of all clones detected). 相似文献
20.
Shwanavidin is an avidin-like protein from the marine proteobactrium Shewanella denitrificans, which exhibits an innate dimeric structure while maintaining high affinity toward biotin. A unique residue (Phe-43) from the L3,4 loop and a distinctive disulfide bridge were shown to account for the high affinity toward biotin. Phe-43 emulates the function and position of the critical intermonomeric Trp that characterizes the tetrameric avidins but is lacking in shwanavidin. The 18 copies of the apo-monomer revealed distinctive snapshots of L3,4 and Phe-43, providing rare insight into loop flexibility, binding site accessibility, and psychrophilic adaptation. Nevertheless, as in all avidins, shwanavidin also displays high thermostability properties. The unique features of shwanavidin may provide a platform for the design of a long sought after monovalent form of avidin, which would be ideal for novel types of biotechnological application. 相似文献