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81.
Clues from Xanthomonas campestris about the evolution of aromatic biosynthesis and its regulation 总被引:4,自引:0,他引:4
R J Whitaker A Berry G S Byng M J Fiske R A Jensen 《Journal of molecular evolution》1984,21(2):139-149
The recent placement of major Gram-negative prokaryotes (Superfamily B) on a phylogenetic tree (including, e.g., lineages leading to Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus) has allowed initial insights into the evolution of the biochemical pathway for aromatic amino acid biosynthesis and its regulation to be obtained. Within this prokaryote grouping, Xanthomonas campestris ATCC 12612 (a representative of the Group V pseudomonads) has played a key role in facilitating deductions about the major evolutionary events that shaped the character of aromatic biosynthesis within this grouping. X. campestris is like P. aeruginosa (and unlike E. coli) in its possession of dual flow routes to both L-phenylalanine and L-tyrosine from prephenate. Like all other members of Superfamily B, X. campestris possesses a bifunctional P-protein bearing the activities of both chorismate mutase and prephenate dehydratase. We have found an unregulated arogenate dehydratase similar to that of P. aeruginosa in X. campestris. We separated the two tyrosine-branch dehydrogenase activities (prephenate dehydrogenase and arogenate dehydrogenase); this marks the first time this has been accomplished in an organism in which these two activities coexist. Superfamily B organisms possess 3-deoxy-D-arabino-heptulosonate 7-P (DAHP) synthase as three isozymes (e.g., in E. coli), as two isozymes (e.g., in P. aeruginosa), or as one enzyme (in X. campestris). The two-isozyme system has been deduced to correspond to the ancestral state of Superfamily B. Thus, E. coli has gained an isozyme, whereas X. campestris has lost one. We conclude that the single, chorismate-sensitive DAHP synthase enzyme of X. campestris is evolutionarily related to the tryptophan-sensitive DAHP synthase present throughout the rest of Superfamily B. In X. campestris, arogenate dehydrogenase, prephenate dehydrogenase, the P-protein, chorismate mutase-F, anthranilate synthase, and DAHP synthase are all allosteric proteins; we compared their regulatory properties with those of enzymes of other Superfamily B members with respect to the evolution of regulatory properties. The network of sequentially operating circuits of allosteric control that exists for feedback regulation of overall carbon flow through the aromatic pathway in X. campestris is thus far unique in nature. 相似文献
82.
L. S. Jensen G. L. Colnago K. Takahashi Y. Akiba 《Biological trace element research》1986,10(1):11-18
Experiments were conducted to study the effect of marginal levels of selenium and vitamin E on plasma thyroid hormones of
meattype chicks. Plasma thyroxine (T4) was significantly increased when a semipurified diet was supplemented with either selenium or vitamin E. Triiodothyronine
(T3) was also significantly increased by vitamin E and in one experiment with selenium supplementation. No significant increase
in these hormones was observed in birds fed a corn-soybean-meal diet supplemented with these nutrients. Plasma corticosterone
level was reduced and weight of the bursa of Fabricius increased by selenium or vitamin E supplementation. These nutrients
may be necessary for providing the optimum thyroid conditions for activity of thyroid peroxidase. 相似文献
83.
Cerebrospinal fluid (CSF) from patients without neurological disorder was analyzed after Sep-Pak extraction for beta-endorphin (beta-EP)-immunoreactive components by combined reversed-phase high-performance liquid chromatography (HPLC) and radioimmunoassay. A C-terminal directed antibody detected one major immunoreactive component, probably identical with beta-EP1-31. An N-terminal directed antibody detected several immunoreactive components. One co-eluted with beta-EP1-31 but the others are probably C-terminal truncated or otherwise modified forms of beta-EP1-31. However, they eluted differently from beta-EP1-16 (alpha-endorphin), beta-EP1-26, 1-27 and alpha,N-acetyl-beta-EP1-31. Alternatively, some of the fragments may represent C-terminal extended forms of pro-enkephalin A-derived Met-enkephalin. A Met-enkephalin antiserum detected several immunoreactive components probably representing N-terminal extended forms; neither of them were identical with the beta-EP-immunoreactive components. The results illustrate the heterogeneity of the beta-EP-immunoreactive components in CSF and the need to characterize the beta-EP radioimmunoassay before its application to biological extracts. 相似文献
84.
Five strains of pink-pigmented, facultatively methylotrophic bacteria (PPFM) isolated from plant surfaces and grown in different carbon sources, were fixed, embedded and sectioned for examination with the electron microscope. The strains studied represented the two mainsub-groups, those that can use carbohydrates and those that can not use carbohydrates as a sole carbon and energy source. All of the isolates examined, produced crystalloid inclusions, internal membranous vesicles and internal membranous sheets although the number of cells with inclusions, varied with the carbon source and specific strain. Polybetahydroxybutyrate and polyphosphate bodies were observed in all strains, with all carbon sources used for growing cells which includes methanol, formate and glycerol. Isolates that could use glucose accumulated polyglucoside granules but not when other carbon sources were provided. The relationship of these inclusions to growth conditions is discussed. 相似文献
85.
Steen Kølvraa Torben A. Kruse P. K. A. Jensen Kirsten H. Linde Søren R. Vestergaard Lars Bolund 《Human genetics》1986,74(3):284-287
Summary EDA (ectodermal dysplasia, anhidrotic) is an X-linked recessive disorder characterized by hypohidrosis, hypoor anodontia, and hypotrichosis. A possible linkage between the gene for EDA and a number of restriction fragment length polymorphisms (RFLPs) spread over the X chromosome was investigated in two Danish families segregating EDA. No recombination between the gene for EDA and our probe pTAK8, which detects a two allele polymorphism in the region Xp11-q12, was found in nine informative meiotic events (seven of which are phase known), giving a maximal lod score of 2.41 at a recombination fraction of 0.00. This juxtacentromeric location of the gene for EDA agrees well with the linkage data obtained with the other markers used in this study. 相似文献
86.
Partial purification and characterization of isopenicillin N epimerase activity from Streptomyces clavuligerus 总被引:2,自引:0,他引:2
Epimerase activity, which converts isopenicillin N to penicillin N, has been partially purified from cell-free extracts of Streptomyces clavuligerus. No stimulating cofactors of this activity were found, and neither EDTA nor anaerobic incubation caused significant inhibition of activity. Although pyridoxal phosphate did not stimulate epimerase activity, the presence of this cofactor was necessary for the stabilization of enzymic activity during the purification process. Epimerase activity was purified 35.5-fold by a combination of salt precipitation, gel filtration, and ion exchange chromatography. Gel filtration indicated that the epimerase has a molecular weight of 60 000 and sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the 35.5-fold purified epimerase showed a major protein band running near that location. Pyridoxal phosphate antagonists did not uniformly inhibit epimerase activity, but the inhibitory effect of hydroxylamine could be partially reversed by pyridoxal phosphate. 相似文献
87.
Thomas T. Stevenson Richard H. Furneaux David Pang Fred Shafizadeh Lyle H. Jensen Ronald E. Stenkamp 《Carbohydrate research》1983,112(2):179-187
A single-crystal, X-ray diffraction study was performed on a nonalkenic, cyclic trimer (C18H18O9, 4) of levoglucosenone, in order to confirm its chemical structure. Crystals of 4 are orthorhombic, with unit-cell parameters of a = 792.20, b = 1874.35, c = 2383.02 pm, space group P212121, and z = 8. The structure was solved by direct methods, and refined by least-squares to R = 0.032, based on 2990 unique reflections. Each asymmetrical unit contains two symmetry-independent molecules of 4 and one of acetone. The previously assigned chemical structure and stereochemistry of 4 were found to be correct. 相似文献
88.
J Cline B Reinhammar P Jensen R Venters B M Hoffman 《The Journal of biological chemistry》1983,258(8):5124-5128
A new rhombic EPR signal was recently discovered in the partially reduced type 2 copper-depleted Rhus vernicifera laccase (Reinhammar, B. (1983) J. Inorg. Biochem., in press). The signal originates from one of the type 3 Cu(II) ions that becomes EPR-detectable as a result of the selective reduction of the other copper ion in the exchange-coupled Cu(II)-Cu(II) pair. The 14N and 1H and 63,65Cu electron nuclear double resonance (ENDOR) of this uncoupled Cu(II) now have been collected and represent the first ENDOR measurements of a type 3 copper site. The data indicate that the copper is coordinated by at least three nitrogenous ligands, at least one of which is an imidazole. H/D exchange suggests a nearby H2O or OH-, perhaps as a fourth ligand. A similar EPR signal is seen for CuB of reduced cytochrome c oxidase under turnover conditions. The 14N ENDOR, and, therefore, the structure, of this site corresponds extremely closely to that of the laccase type 3 (Cu(II). 相似文献
89.
Suspensions of mesophyll cells, prepared from tobacco leaves by treatment with pectinase, fixed CO2 by photosynthesis. The products of carbon assimilation were similar for both cells and intact tissue. The cells sustained a constant fixation rate for 20 to 25 hours. For optimal CO2 fixation, enzymatic maceration of the tissue was accomplished in 0.8 m sorbitol, but photosynthesis was optimal in 0.6 m sorbitol at pH 7 to 7.5. A hypertonic environment during maceration, which results in cell plasmolysis, is essential to maintain intact plasmalemmas and hence photosynthetically active cells. For sustained CO2 fixation, light intensities below 500 foot-candles were required. Higher light intensities (to 1000 foot-candles) gave high initial rates of CO2 fixation, but the cells bleached and were inactive on prolonged incubation. At pH 7.0 the bicarbonate concentration at maximal velocity of CO2 fixation was about 1.5 mm and the apparent Km for bicarbonate was 0.2 mm. 相似文献
90.
Thomas Lynch (1971) has recently attempted to document the fact that the preceramic hunter-gatherers of Peru were mobile throughout a range of altitudinal zones and that the fields of movement of these preceramic populations may well have been continuous, since the members of each group exploited the resources of different habitats in terms of regular annual cycles. However, it is equally clear that these long, linear fields of the preceramic populations began to be fragmented at some point in lime. We believe that the termination of the proposed period of transhumance constitutes an extremely interesting problem. At the present time this feature has been discussed only in terms of data from the Peruvian coast. In this paper we employ some of Lynch’s data and observations in an attempt to demonstrate (I) that a minimum of modification of the preceramic pattern of food procurement within the highlands was required to convert hunter-gatherers into food producers; and (2) wild tubers played a crucial role in this process. 相似文献