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981.
The aerobic microbial decomposition of trichloroacetic acid (TCA) was studied. A TCA-decomposing culture was enriched in continuous-flow and batch experiments on a medium containing TCA as the only organic component. Pure cultures of TCA degraders were isolated from the enrichment on TCA agar plates. Characterization of several isolates proved them all to be representatives of the same bacterium, a Gram-negative, catalase-positive and cytochrome C-oxidase-positive, non-motile, somewhat irregular rod. The bacterium could not be identified on the basis of its carbon-source-utilization pattern, but a partial sequencing of the 16S rDNA gene showed the isolate to belong to the gamma sub-group of Proteobacteria, and to be phylogenetically close to Acinetobacter calcoaceticus. The isolated bacterium grew exponentially with TCA as the sole source of energy and carbon. The maximum growth rate (µmax) and the growth yield on TCA (Y
X/S
) were determined to be 0.027 h–1 and 0.027 g biomass/g TCA, respectively. The bacterium was not able to grow on mono- or dichloroacetic acid, but it could grow on acetate. 相似文献
982.
983.
984.
绞股蓝属的染色体研究 总被引:11,自引:2,他引:9
报道了葫芦科绞股蓝属(Gynostemma B1.)8种共20个居群的染色体数目,分别为2n=22,33,44,66,88多倍体现象极为普遍。两个亚属;绞股蓝亚属(Subgen.Gynostemma)和喙果藤亚属(Subgen.Triostellum)的染色体基数均为X=11,并结合该属植物形态特征、繁殖方式和地理分布,对普遍出现的多倍体现象进行了讨论。 相似文献
985.
Lenzi Kaden Armando J. L. Pombeiro Yu Wang Ulrich Abram 《Inorganica chimica acta》1995,230(1-2):189-192
The Tc(I) mixed-ligand complex, trans-[Tc(dppe)2(butNC)2](PF6) (dppe=bis(diphenylphosphino)ethane, butNC=tert-butyl-isocyanide) has been prepared from [Tc(tu−S)63+ (tu-S=thiourea) and a mixture of both ligands. The compound crystallizes triclinic in the space group ). The technetium atom has a slightly distorted octahedral coordination sphere with the isocyanide ligands in trans-position to each other. By cyclic voltammetry, at a Pt electrode, trans-[Tc(dppe)2(butNC)2](PF6) undergoes a single electron reversible oxidation at E1/2ox=0.91 V versus SCE. 相似文献
986.
Oligoribonuclease, an exoribonuclease specific for small oligoribonucleotides, was initially characterized 20 years ago (S. K. Niyogi and A. K. Datta, J. Biol. Chem. 250:7307-7312, 1975) and shown to be different from RNase II and polynucleotide phosphorylase. Here we demonstrate, using mutant strains and purified enzymes, that oligoribonuclease is not a manifestation of RNases D, BN, T, PH, and R, exoribonucleases discovered subsequently. Thus, oligoribonuclease is the eighth distinct exoribonuclease discovered in Escherichia coli. We also show that oligoribonuclease copurifies with polynucleotide phosphorylase. 相似文献
987.
988.
P Zhong S D Pratt R P Edalji K A Walter T F Holzman A G Shivakumar L Katz 《Journal of bacteriology》1995,177(15):4327-4332
ErmC' is a methyltransferase that confers resistance to the macrolide-lincosamide-streptogramin B group of antibiotics by catalyzing the methylation of 23S rRNA at a specific adenine residue (A-2085 in Bacillus subtilis; A-2058 in Escherichia coli). The gene for ErmC' was cloned and expressed to a high level in E. coli, and the protein was purified to virtual homogeneity. Studies of substrate requirements of ErmC' have shown that a 262-nucleotide RNA fragment within domain V of B. subtilis 23S rRNA can be utilized efficiently as a substrate for methylation at A-2085. Kinetic studies of the monomethylation reaction showed that the apparent Km of this 262-nucleotide RNA oligonucleotide was 26-fold greater than the value determined for full-size and domain V 23S rRNA. In addition, the Vmax for this fragment also rose sevenfold. A model of RNA-ErmC' interaction involving multiple binding sites is proposed from the kinetic data presented. 相似文献
989.
Abstract: The weaver mutant mouse (wv/wv) has an ~70% loss of nigrostriatal dopamine (DA) neurons, but the fractional DA release evoked by amphetamine (but not a high potassium level) has been shown to be greater from striatal slices of the weaver compared with +/+ mice. In the present work we tested the hypothesis that fractional DA release from weaver striatum would be greater when release was mediated by the DA transporter. Serotonin (5-HT)-stimulated fractional DA release was greater from weaver than from +/+ striatum. The release evoked by 5-HT in the presence of 10 µM nomifensine (an antagonist of the DA transporter) was less than in its absence, but the difference between weaver and +/+ striatum remained. In the presence of nomifensine, 1-(m-chlorophenyl)biguanide, classified as a 5-HT3 agonist, also induced a greater fractional release from weaver compared with +/+ striatum. When veratridine was used at a low concentration (1 µM), the fractional evoked release of DA was higher from the weaver in the presence and absence of nomifensine. These findings suggest that the reason for the difference in the responsiveness of the two genotypes to these release-inducing agents is not related to DA transporter function. 相似文献
990.
Evaluation of cellulase recycling strategies for the hydrolysis of lignocellulosic substrates 总被引:8,自引:0,他引:8
Recycling of cellulases should lower the overall cost of lignocellulosiic bioconversion processes. In this study, three recycling strategies were evaluated to determine their efficiencies over five successive rounds of hydrolysis. The effect of lignin on recycling was examined by comparing water-washed, steam-exploded birch (WB; 32% lignin) and WB which had been further extracted with alkali and peroxide (PB; 4% lignin). When the cellulases were recovered from the residual substrates after partial hydrolysis of both substrates, the recovered cellulase activity toward the mixture of fresh and residual substrates decreased after each recycling step. When the cellulases in the supernatants were also recycled, up to 20% more activity could be recovered. In both of these cases, the recovered activities did not correspond to the activities expected from the amount of cellulase protein recovered during recycling. The best recovery was obtained when the cellulases were recovered from both the residue and the supernatant after complete hydrolysis of the PB substrate. In this case, all of the originally added cellulase activity could be recovered for four consecutive hydrolysis rounds. However, when the same recycling strategy was carried out using the WB substrate, the recovered cellulase activity declined quickly with each recycling round. In all three of the recycling strategies, lower cellulase activities were recovered from the substrates with higher lignin contents. (c) 1995 John Wiley & Sons, Inc. 相似文献