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91.
It was found that crude preparation obtained from the culture medium of Fusarium avenaceum degraded cellulose and xylan. After chromatography on CM-Sepharose CL-6B of this preparation six fraction were obtained. The eluted fractions II and V showed xylanase activity, fraction IV — cellulase activity and fraction III — xylanase and cellulase activity. The end products of xylan hydrolysis by all xylanase fractions (II, III, V) were xylobiose, xylose, xylotriose and xylotetrose. The end products of cellulose hydrolysis by fractions III and IV was cellobiose, glucose and cellotriose. The data from gel filtration on Sephacryl S-200 indicated a molecular weight of more than 250,000 for both cellulase IV and xylanase V. After gel filtration in the presence of urea disaggregation of those high molecular xylanase and cellulase particles was observed. Xylanase II in difference from the other fractions contained higher amount of sugar. Digestion of fraction II with cellulase-hemicellulase preparation from Phoma hibernica decreased the content of sugar from 17% to 8%, but did not change its enzymatic properties. Cellulase IV as well as xylanase V were inactivated by N-bromosuccinimide, 2-hydroxy-5-nitrobenzyl bromide and tetranitromethane, hence it is suggested that tryptophan and tyrosine are the essential for the activity of these enzymes. 相似文献
92.
A.N. Davison 《FEBS letters》1982,144(2):370-371
We have purified a unique enzyme, α-amino-?-caprolactam racemase 945-fold from an extract of Achromobacter obae by Octyl—Sepharose CL-4B and Thiopropyl—Sepharose 6B and some other chromatographies. The purified enzyme was found homogeneous by sodium dodecyl sulfate—polyacrylamide gel electrophoresis and analytical ultracentrifugation. The enzyme has a monomeric structure with Mr ~ 50 000 and a sedimentation coefficient (s20,w) of 4.28 S. The enzyme contains pyridoxal 5'-phosphate as a coenzyme. The pH optimum for the enzyme activity is ~9.0. D- and L-α-amino-?-caprolactams are the only substrates. The Km values for the D- and L-isomers are, 8 and 6 mM, respectively. 相似文献
93.
Two types of amino acid substitutions in protein evolution 总被引:35,自引:0,他引:35
Summary The frequency of amino acid substitutions, relative to the frequency expected by chance, decreases linearly with the increase in physico-chemical differences between amino acid pairs involved in a substitution. This correlation does not apply to abnormal human hemoglobins. Since abnormal hemoglobins mostly reflect the process of mutation rather than selection, the correlation manifest during protein evolution between substitution frequency and physico-chemical difference in amino acids can be attributed to natural selection. Outside of abnormal proteins, the correlation also does not apply to certain regions of proteins characterized by rapid rates of substitution. In these cases again, except for the largest physico-chemical differences between amino acid pairs, the substitution frequencies seem to be independent of the physico-chemical parameters. The limination of the substituents involving the largest physicochemical differences can once more be attributed to natural selection. For smaller physico-chemical differences, natural selection, if it is operating in the polypeptide regions, must be based on parameters other than those examined. 相似文献
94.
The damping mechanisms that are operational in the heel pad during the impact phase of locomotion have the important function to protect the musculo-skeletal system from injuries. How this is achieved is still not fully understood, as is for instance illustrated by the ‘heel pad paradox’, the observation that in vivo and in vitro experiments yielded widely different results. This paradox could so far only partially be explained. In the light of this paradox, and a previous study by our group, we conjectured that the venous plexus might contribute as a hydraulic shock absorber to the damping properties of the heel pad. To investigate this hypothesis in vivo, heel pads of 11 volunteers were subjected to pendulum impact tests, using velocities of 0.2, 0.4, and 0.6 m/s, and three physiologically different, consecutive conditions: (i) a relatively empty venous plexus, (ii) a congested venous plexus, and (iii) a decongested venous plexus. At congestion, the maximum impact force decreased slightly but significantly by 2.6% at 0.2 m/s and 1.8% at 0.4 m/s. This effect was no longer found at 0.6 m/s. Although these effects are rather small, they confirm the fundamental hypothesis that the venous plexus contributes to the damping properties of the heel pad during walking. It is likely that some underestimation of the effect has occurred. 相似文献
95.
从表现褪绿条纹花叶症状的小苍兰(Freesia hybrida)上分离得到一种棒状病毒,能感染茄科、藜科、苋科、玄参科和葫芦科的部分植物。病毒粒子长500—575nm,直径13nm。外壳蛋白由一种分子量17500dalton的蛋白亚基组成。纯化的病毒制剂具有典型的核蛋白紫外吸收,A260/A280为1.39。稀释终点10~(-7),致死温度约为95℃,在4℃下体外保毒期大于6个月。排蚜不能传毒。病毒与PVX有血清学关系。实验表明,该病毒属于马铃薯X病毒群,不同于已报道的感染小苍兰的其它病毒。本文还讨论了小苍兰褪绿条纹花叶病毒的控制和检测问题。 相似文献
96.
97.
One-dimensional lanthanide-ferrocenesuccinate polymeric complexes [M(η2-FcCOC2H4COO)(μ2-η2-FcCOC2H4COO)2(H2O)2]n (Fc = (η5-C5H4)Fe(η5-C5H4), M = Pr, 1; Ce, 2; La, 3) have been synthesized and structurally characterized by single-crystal X-ray crystallography. The three polymers are isomorphous, in which each Ln(III) ion is 10-coordinated and connects with two water molecules and eight oxygen atoms from ferrocenesuccinate units in two kinds of coordination modes: bidentate-chelating mode and tridentate-bridging mode. The variable-temperature magnetic susceptibility in the temperature range 5-300 K for 1 and 2 shows that both of them display weak antiferromagnetic interaction. In addition, the redox and fluorescent properties have been investigated. The redox properties are different from the previous results of transition metal compounds containing ferrocenyl systems. Compared with sodium ferrocenesuccinate, polymers 1 and 3, the fluorescent intensities of 2 are markedly enhanced in the solid state. 相似文献
98.
G. Ferretti C. Marchionni T. Bacchetti T. Galeazzi N. Dousset 《Free radical research》2013,47(5):515-521
We investigated the effect of aluminium (Al 3+ ) on lipid peroxidation and physico-chemical properties of high density lipoproteins (HDL) isolated from human plasma. Our results demonstrated that Al 3+ enhances lipid peroxidation of human HDL as shown by the significant increase in lipid hydroperoxides in Al-treated HDL with respect to control HDL. The oxidative effect was higher at acid pH (pH 5.5) with respect to pH 7.4. Moreover, a stimulating effect of Al 3+ on iron-induced lipid peroxidation of HDL was demonstrated. The study of the effect of Al 3+ on the physico-chemical properties of HDL, using the fluorescence polarization (Pf) of the probes TMA-DPH (1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) and DPH (1,6-diphenyl-1,3,5-hexatriene), showed a significant decrease of Pf in Al-treated HDL with respect to control. These results suggest that Al 3+ induces a decrease of molecular order at the lipoprotein surface. Moreover, the study of tryptophan (Trp) fluorescence demonstrated that aluminium induces structural modifications of HDL apoproteins and on HDL physico-chemical properties. The effect of Al 3+ on lipid peroxidation of HDL was observed at aluminium concentrations similar to those observed in the brain of patients affected by neurological diseases. Aluminium-induced oxidative damage of HDL could be involved in the development of neurological diseases. 相似文献
99.
《Journal of biological education》2012,46(2):141-143
The use of an imaginary organism to illustrate principles of genetics is described. The organism is easily drawn, and is well suited to simple printing techniques. It has been used to show independent segregation of genes, partial dominance, linkage in both sex chromosomes and in autosomes, as well as the inheritance of an autosomal gene lethal in the homozygous state. Additional exercises for students are suggested. 相似文献
100.
Influence of silicone oil modification on properties of ramie fiber reinforced polypropylene composites 总被引:1,自引:0,他引:1
This paper focused on the analyses of the composition, microstructure, thermal stability and mechanical behavior of modified ramie fiber and its reinforced polypropylene composites. Ramie fiber (RF) was treated with epoxy-silicone oil (ESO) at 160 °C in argon gas. The FTIR and XRD analyses indicated that some silicone molecular chains were bonded on the surface of modified RF, which decreased the crystallinity of the fiber without changing the crystalline type of cellulose. The SEM results of fracture surface showed that the modified RF/PP composite had better interfacial bonding between RF and PP. The mechanical tests showed that the impact strength and the elongation at break of RF/PP were increased by 17.0% and 196% after modification, respectively. The tensile strength of 30RF/PP was improved from 18.95 MPa to 25.96 MPa compared to pure PP. The results of TGA showed that fiber treatment could improve the degradation temperature of RF/PP composites. 相似文献