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101.
1,3-β-Glucan synthase activity has been demonstrated in particulate fractions of bark extracts from Mexican lime. With respect to substrate, the enzyme kinetics did not conform to the Michaelis-Menten equation. The value of the Hill coefficient was 1.2 and S0.5 is 1.1 mM. The enzyme had an optimum pH of 7.5. Maltose, sucrose, and especially cellobiose and glucose, were enzyme activators when tested at physiological concentrations. In the presence of 15 mM MgCl2 the enzymic activity was stimulated at 10 μM UDP-glucose but decreased at 1 mM UDP-glucose, suggesting a minor 1,4-β-glucan synthase activity. 相似文献
102.
Methods für the determination of urinary free corticosterone, free aldosterone and free 11-deoxycorticosterone (DOC) in rats are described. The free corticosteroids were measured in urine samples of 0.1–0.5 (2.0) ml by radioimmunoassay after purification by column chromatography. The validity of the methods is demonstrated by the data of the free urinary corticoids under basal conditions and after adrenal suppression and various forms of adrenal stimulation. The basal excretion of free corticosterone, free aldosterone and free DOC was 123.71 ± 15.31 (x? ± SD), 3.87 ± 1.29 and 10.61 ± 2.24 ng/day, respectively, exhibiting a decrease to 26.20 ± 5.21, 1.05 ± 0.47 and 1.35 ± 1.20 ng/day after adrenal suppression by dexamethasone. Irrespective of the mode of adrenal stimulation i.e., synthetic ACTH and systemic (cold, hunger) or neurotrophic (ether, reserpine) stress stimuli free corticosterone increased to about 450 ng/day, while free aldosterone excretion decreased during hunger and cold and was strongly enhanced after the application of reserpine. Furthermore, determination of urinary free DOC, which increased by a factor of 4, may be applied in the metyrapone test. There was a good correlation between the excretion of free corticosterone and that of free aldosterone and free DOC under basal conditions and after ACTH application, demonstrating that ACTH is responsible for the secretion of all the 3 corticoids measured. It is concluded, that the measurement of the urinary excretion of corticosterone, aldosterone and DOC is a valuable parameter of adrenal function in rats. Furthermore, in small laboratory animals like rats steroid measurements in urine are often more advantageous than Measurements in plasma. 相似文献
103.
16alpha-Hydroxyandrostenedione (16alpha-hydroxyandrost-4-ene-3,17-dione), 16alpha-hydroxytestosterone (16alpha,17beta-dihydroxyandrost-4-en-3-one) and 16alpha-hydroxydehydroepiandrosterone 3-sulfate (3beta, 16alpha-dihydroxyandrost-5-en-17-one 3-monosulfate) were synthesized by a new chemical approach with much improved yield. 16alpha-Bromoandrostendione was converted to the hydrazone of 16alpha-hydroxyandrostenedione which gave 16alpha-hydroxyandrostenedione on acid hydrolysis in total 63% yield. Oxidation of 16alpha-hydroxydehydroepiandrosterone with Jones' reagent also selectively afforded 16alpha-hydroxyandrostenedione. 16alpha-Hydroxytestosterone was observed by selective reduction of 16alpha-hydroxyandrostenedione with sodium borohydride. Reaction of 16alpha-hydroxydehydroepiandrosterone with chlorosulfonic acid in pyridine selectively gave the 3-monosulfate. The structure of the sulfate was deduced from its solvolysis to the starting material, and its acetylation and subsequent solvolysis to 16alpha-hydroxydehydroepiandrosterone 16-acetate. All procedures are suitable for large scale synthesis without the use of microorganisms. 相似文献
104.
Under the protection of ascorbic acid a 2-hydroxyestrone bovine serum albumin conjugate was prepared containing intact 2-hydroxyestrone as determined by gas chromatographymass spectrometry. Using this antigen highly specific antibodies were raised in rabbits. Cross-reactivity for 2-hydroxyestradiol and 2-hydroxyestriol was 26 and 4.5%, respectively. An assay procedure of 2-hydroxyestrone in human plasma is described. Using special precautions the assay allows the determination of 2-hydroxyestrone in plasma samples of women (50–95 pg/ml), pregnant women (105–220 pg/ml), men (45–65 pg/ml) and children (20–40 pg/ml). 相似文献
105.
Treatment of 8-9-day-old C57BL/A mice with a single carcinogenic dose of urethane, at 1.2 mg/g body wt., resulted in an immediate decrease in liver DNA synthesis reaching a maximum at about 16-18 h after injection, the rate of synthesis returning to normal after 48 h. When the nuclear proteins were radiolabelled, the non-histone protein (NHP) fraction showed a significant decrease in specific activity 8-18 h after injection of urethane and slight increase in specific activity after 24 h. Histone and residual proteins did not show any significant change. The liver NHP were analysed by isoelectric focusing (IEF) and sodium dodecyl sulphate (SDS) electrophoresis in polyacrylamide gels. The latter technique failed to show any distinctive differences but IEF results indicated some quantitative and qualitative changes in protein content and synthesis were induced by the urethane treatment. The most noticeable change in the stained gels was an increase in a protein component having a pI of 7.35 and the appearance of new bands at pI's of 7.85 and 5.55 in the 18 h treated livers. However, the [3H]tryptophan labelling pattern indicated that this was not due to an increased synthesis of these components. 24 h after urethane there appeared to be an increased rate of synthesis of some of the major components of the mixture, particularly at the pI 5.65 region. Histone and residual protein fractions were also analysed by electrophoresis and showed no difference between treated and control livers. 相似文献
106.
107.
Mathias Uhlén Björn Nilsson Bengt Guss Martin Lindberg Sten Gatenbeck Lennart Philipson 《Gene》1983,23(3):369-378
Two plasmid vectors, containing the gene coding for staphylococcal protein A and adapted for gene fusion, have been constructed. These vectors will allow fusion of any gene to the protein A gene, thus giving hybrid proteins which can be purified, in a one-step procedure, by IgG affinity chromatography. As an example of the practical use of such vectors, the protein A gene has been fused to the lacZ gene of Escherichia coli. E. coli strains containing such plasmids produce hybrid proteins with both IgG binding and β-galactosidase activities. The hybrid protein(s) can be immobilized on IgG-Sepharose by its protein A moiety with high efficiency without losing its enzymatic activity and they can be eluted from the column by competitive elution with pure protein A. The fused protein(s) also binds to IgG-coated microtiter wells which means that the in vivo product can be used as an enzyme conjugate in ELISA tests. 相似文献
108.
In rat liver membranes cholera toxin ADP-ribosylated two polypeptides (Mr 42000 and 47000) in the regulatory component of adenylate cyclase. L-arginine methyl ester specifically inhibited both the activation of adenylate cyclase and ADP-ribosylation by cholera toxin, suggesting that cholera toxin modified arginine, or arginine-like, residues. A hydrolysis-resistant analogue of GTP (β, γ-imidoguanosine 5′-triphosphate, p(NH)ppG) bound to the regulatory protein in an essentially irreversible manner. Pretreatment with the analogue failed to inhibit the labelling of polypeptides by cholera toxin showing that the sites for ADP-ribosylation were different from those at which guanyl nucleotides were bound. 相似文献
109.
Cytoplasmic proteases of rat liver parenchymal cells 总被引:2,自引:0,他引:2
G N DeMartino 《Biochemical and biophysical research communications》1982,108(3):1325-1330
Soluble extracts of isolated rat liver parenchymal cells contained three proteases with alkaline pH optima. One protease was a high molecular weight (Mr = 500,000) enzyme which was stimulated by ATP. The other two proteases were totally dependent on calcium for activity and displayed different calcium concentration requirements. One was half-maximally activated by 150 μM Ca2+ while the other required only 10 μM Ca2+ for half-maximal activation. 相似文献
110.
E Melloni B Sparatore F Salamino M Michetti S Pontremoli 《Biochemical and biophysical research communications》1982,107(3):1053-1059
The soluble neutral proteinase of human erythrocytes dissociates into constituent subunits of 80k and 30k in the presence of mM concentrations of Ca2+. Similarly the soluble natural inhibitor of this proteinase, of approximate molecular weight 240k, is dissociated into 60k subunits by mM concentrations of Ca2+. Removal of Ca2+ restores the native oligomeric structure of the proteinase and of the natural inhibitor. The formation of the native active enzyme or of the inactive enzyme-inhibitor complex depends on reversible association-dissociation processes mediated by Ca2+ concentration. 相似文献