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91.
92.
The reductive acetyl coenzyme A pathway: sequence and heterologous expression of active methyltetrahydrofolate:corrinoid/iron-sulfur protein methyltransferase from Clostridium thermoaceticum. 总被引:1,自引:1,他引:0
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The methyltransferase (MeTr) from Clostridium thermoaceticum transfers the N5-methyl group of (6S)-methyltetrahydrofolate to the cobalt center of a corrinoid/iron-sulfur protein in the acetyl coenzyme A pathway. MeTr was purified to homogeneity and shown to lack metals. The acsE gene encoding MeTr was sequenced and actively expressed in Escherichia coli at a level of 9% of cell protein. Regions in the sequence of MeTr and the E. coli cobalamin-dependent methionine synthase were found to share significant homology, suggesting that they may represent tetrahydrofolate-binding domains. 相似文献
93.
Characterization of the interaction of the glp repressor of Escherichia coli K-12 with single and tandem glp operator variants. 总被引:2,自引:2,他引:0
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N Zhao W Oh D Trybul K S Thrasher T J Kingsbury T J Larson 《Journal of bacteriology》1994,176(8):2393-2397
The glp operons of Escherichia coli are negatively controlled by the glp repressor. Comparison of the repressor-binding affinities for consensus and altered consensus operators in vivo showed that all base substitutions at positions 3, 4, 5, and 8 from the center of the palindromic operator caused a striking decrease in repressor binding. Substitutions at other positions had a severe to no effect on repressor binding, depending on the base substitution. The results obtained indicate that the repressor binds with highest affinity to operators with the half-site WATKYTCGWW, where W is A or T, K is G or T, and Y is C or T. Strong cooperative binding of the repressor to tandem operators was demonstrated in vivo. Cooperativity was maximal when two 20-bp operators were directly repeated or when 2 bp separated the two operators. Cooperativity decreased with the deletion of 2 bp or the addition of 4 bp between the individual operators. Cooperativity was eliminated with a 6-bp insertion between the operators. 相似文献
94.
Ten soils collected from the major arable areas in Britain were used to assess the availability of soil sulphur (S) to spring
wheat in a pot experiment. Soils were extracted with various reagents and the extractable inorganic SO4-S and total soluble S(SO4-S plus a fraction of organic S) were determined using ion chromatography (IC) or inductively-coupled plasma atomic emission
spectrometry (ICP-AES), respectively. Water, 0.016 M KH2PO4, 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 extracted similar amounts of SO4-S, as measured by IC, which were consistently smaller than the total extractable S as measured by ICP-AES. The amounts of
organic S extracted varied widely between different extractants, with 0.5 M NaHCO3 (pH 8.5) giving the largest amounts and 0.01 M CaCl2 the least. Organic S accounted for approximately 30–60% of total S extracted with 0.016 M KH2PO4 and the organic C:S ratios in this extract varied typically between 50 and 70. The concentrations of this S fraction decreased
in all soils without added S after two months growth of spring wheat, indicating a release of organic S through mineralisation.
All methods tested except 0.5 M NaHCO3-ICP-AES produced satisfactory results in the regression with plant dry matter response and S uptake in the pot experiment.
In general, 0.016 M KH2PO4 appeared to be the best extractant and this extraction followed by ICP-AES determination was considered to be a good method
to standardise on. 相似文献
95.
96.
97.
Protoplasts isolated from both 7-day-old light-grown and 4-day-old dark/dim light-grown cotyledons of four Brassica campestris varieties (Arlo, Sonja, Bunyip and Wonk Bok) were cultured in three liquid media: modified K8P, modified MS and modified Pelletier's B to compare the capacities for cell division and plant regeneration. Following cell wall regeneration the cultured protoplasts from dark/dim light-grown cotyledons of four varieties showed rapid division and high frequency of cell division compared with those isolated from light-grown cotyledons. The frequencies of cell division were significantly influenced by varieties and culture media but only in cultured protoplasts isolated from dark/dim light-grown cotyledons. The interaction between varieties and media was also significant. Cell colonies formed within 7–14 days in protoplast cultures from dark/dim light-grown cotyledons, and calli subsequently grown on a solid medium developed shoots when transferred onto a regeneration medium. Three of four tested varieties (Arlo, Sonja and Bunyip) showed shoot regeneration within 2–3 months after protoplast isolation, with a high degree of reproducibility in Arlo and Bunyip. Regenerated shoots, which were induced to root on half-strength MS medium with 0.1 mg.l–1 IBA, survived in soil and grew to produce siliques and set viable seeds in the greenhouse. The present report is the first to document the production of regenerated plants that set seeds in Brassica campestris from cotyledonary protoplasts.Abbreviations BAP
benzylaminopurine
- CPW
Composition of Protoplast Washing-solution
- 2,4-D
2,4-dichlorophenoxyacetic acid
- EDTA
ethylenediamine-tetraacetic acid
- GA3
gibberellic acid
- IBA
indole-3-butyric acid
- IAA
indole-3-acetic acid
- MS
Murashige and Skoog medium
- NAA
-naphthaleneacetic acid
- KT
kinetin
- FDA
fluorescein diacetate
- SDS
sodium dodecyl sulfate 相似文献
98.
Zhao Ying Hiromasa Tojo Takanori Komatsubara Manabu Nakagawa Masami Inada Sumio Kawata Yuji Matsuzawa Mitsuhiro Okamoto 《生物化学与生物物理学报:疾病的分子基础》1994,1226(2):201-205
Enzyme activity, protein contents, and mRNA contents of group II phospholipase A2 (PLA2) in hepatocellular carcinoma (HCC) surgically obtained from 8 patients were compared with those in either its neighboring liver tissues or control liver tissues. The PLA2 specific activity towards the mixed micelles of 1-palmitoyl-2-oleoyl-phosphatidylglycerol and cholate was significantly greater in the tumor tissues (6.62 ± 1.46 nmol/min/mg) than those in the surrounding liver tissues (1.33 ± 0.22 nmol/min/mg) and controls (0.43 ± 0.04 nmol/min/mg). The results of immunoblot analysis using a specific anti-human group II PLA2 antibody and of Northern blot analysis using a human group II PLA2 cDNA as a probe demonstrated that group II PLA2 was responsible for the increased enzyme activity. The contents of immunoreactive group II PLA2 in the tumor tissues (8.81 ± 1.24 ng/mg) were significantly higher than those in the surrounding liver tissues (1.77 ± 0.27 ng/mg); those in the control tissues were below the analytical range of the method used. The group II PLA2 mRNA was also significantly increased in the tumor tissues, compared with that in the surrounding liver tissues, whereas it was not detectable in th controls. This indicates that group II PLA2 in HCC is induced at the pretranslational level. 相似文献
99.
马蹄香大小孢子发生及雌雄配子体形成 总被引:1,自引:0,他引:1
马蹄香(Sarumahenryi,Oliv.)花药壁的发育属双子叶型。花粉母细胞减数分裂为同时型,四分体主要为四面体形,少数为左右对称式排列。腺质绒毡层,其细胞可排列为不规则的两层,双核或多核。到单细胞花粉阶段,绒毡层细胞内切向壁上出现许多乌氏体。成熟花粉为2细胞型,圆球状,具单萌发沟。雌蕊6心皮,上部彼此分离、下部联合。倒生胚珠,双珠被,厚球心。胚囊发育蓼型。成熟胚囊为七细胞结构,但两个助细胞退化较早。 相似文献
100.