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11.
Centrifugal column chromatography was shown to provide a rapid, efficient, and useful means of separation of various low molecular weight thiols from proteins. The single chromatographic step procedure employed standard 5 ml plastic syringes containing Sephadex G-25 as the bed matrix and required less than 5 min to produce average dilutions of 5000-, 980-, and 25-fold, respectively, from 5 to 200 mM initial concentrations of 2-mercaptoethanol, dithiothreitol, and reduced glutathione in the sample as measured by titration with 5,5'-dithiobis-(2-nitrobenzoic acid). Dihydrofolate reductase solutions of 0.07-0.08 mM were separated from 50 mM 2-mercaptoethanol, dithiothreitol, or reduced glutathione with a minimum 16,500-fold dilution of the thiol after centrifugal chromatography on two consecutive columns. Thymidylate synthase solutions of 0.06 mM were effectively separated from 50 mM 2-mercaptoethanol or dithiothreitol with a minimum average 5900-fold dilution of the thiol after consecutive column chromatography. There was no change in either the physical or chemical properties of the enzyme throughout the course of the experiments as determined by activity, active site sulfhydryl group titration, and binding assays. Recoveries of protein obtained in the load fraction were usually in excess of 70% of the protein loaded with virtually no dilution from the initial concentration. This method was developed in order to facilitate the study of the active site sulfhydryl groups in enzymes. 相似文献
12.
G F Watts W Ahmed J Quiney R Houlston P Jackson C Iles B Lewis 《BMJ (Clinical research ed.)》1988,296(6617):235-237
The plasma lipid and lipoprotein responses to two modified isoenergetic diets including meat were studied in 15 free living men with hyperlipidaemia (mean plasma cholesterol and triglyceride concentrations 8·1 and 3·4 mmol/l). A reference diet (diet A, 42% energy from fat, ratio of polyunsaturated to saturated fatty acids (P:S ratio) 0·2) was compared with a fat reduced diet (diet B, 35% energy from fat, P:S ratio 0·5) and with a further fat modified diet supplemented with fibre (diet C, 27% energy from fat, P:S ratio 1·0). Daily intake of meat and meat products (180 g/day) was the same in each dietary period; that in diet A had a fat content typical of the average British diet, whereas that in diets B and C was based on very lean meat and meat products. During consumption of diet B the plasma cholesterol concentration fell by 8·6% and low density lipoprotein cholesterol by 11%. During consumption of diet C plasma cholesterol fell by 18·5% and low density lipoprotein cholesterol by 23·8%. Triglyceride and high density lipoprotein cholesterol concentrations and body weight did not change appreciably during the study.A modified diet including a moderate amount of lean meat and meat products is compatible with a reduced lipoprotein mediated risk of atherosclerotic heart disease. 相似文献
13.
Molecular basis of organ-specific selection of viral variants during chronic infection. 总被引:19,自引:16,他引:3 下载免费PDF全文
R Ahmed C S Hahn T Somasundaram L Villarete M Matloubian J H Strauss 《Journal of virology》1991,65(8):4242-4247
Viral variants of different phenotypes are present in the central nervous system (CNS) and lymphoid tissues of carrier mice infected at birth with the Armstrong strain of lymphocytic choriomeningitis virus. The CNS isolates are similar to the parental virus and cause acute infections in adult mice, whereas the lymphoid isolates cause chronic infections associated with suppressed T-cell responses. In this study, we provide a molecular basis for this organ-specific selection and identify a single amino acid change in the viral glycoprotein that correlates with the tissue specific selection and the persistent and immunosuppressive phenotype of the variants. This phenylalanine (F)-to-leucine (L) change at position 260 of the viral glycoprotein was seen in the vast majority (43 of 47) of the lymphoid isolates, and variants with L at this residue were selected in spleens of persistently infected mice. In striking contrast, isolates with the parental sequence (F at residue 260) predominated (48 of 59 isolates) in the CNS of the same carrier mice. Complete nucleotide sequence analysis of the major structural genes of several independently derived (from different mice) spleen isolates showed that these variants were greater than 99.8% identical to the parental virus. In fact, the only common change among these spleen isolates was the F----L mutation at residue 260 of the glycoprotein. These results show that an RNA virus can exhibit minimal genetic drift during chronic infection in its natural host, and yet a single or few mutations can result in the organ-specific selection of variants that are markedly different from the parental virus. 相似文献
14.
Site-directed mutagenesis of the alpha subunit of tryptophan synthase from Salmonella typhimurium 总被引:1,自引:0,他引:1
S A Ahmed H Kawasaki R Bauerle H Morita E W Miles 《Biochemical and biophysical research communications》1988,151(2):672-678
Site-specific mutagenesis has been used to prepare two mutant forms of the alpha subunit of tryptophan synthase from Salmonella typhimurium in which either cysteine-81 or cysteine-118 is replaced by a serine residue. These mutant proteins are potentially useful for x-ray crystallographic studies since a heavy metal binding site is specifically eliminated in each mutant. The purified mutant proteins are fully active in four reactions catalyzed by the wild type alpha 2 beta 2 complex of tryptophan synthase. However, the mutant alpha 2 beta 2 complexes dissociate more readily and are less heat-stable than the wild type alpha 2 beta 2 complex. Thus, cysteine-81 and cysteine-118 of the alpha subunit serve structural but not functional roles. 相似文献
15.
The neem tree (Azadirachta indica) contains promising pest-control substances found effective against many economically important pests. These materials are easy to process by village-level industries and easy to use by limited-resource farmers, thereby offering potential for crop protection and off-farm income generation. The tree’s numerous pharmacological and other complementary uses make it doubly attractive for incorporation in large-scale rural development efforts. 相似文献
16.
Two nuclear cAMP-independent protein kinases (designated PK-N1 and PK-N2) were purified from rat ventral-prostate and liver. The yield of enzyme units was 4-5% and 7-9% for each enzyme from the prostatic nuclei and liver nuclei, respectively. The average fold purification for prostatic nuclear protein kinase N1 and N2 was 1360 and 1833, respectively. The respective average specific activity of the two enzymes towards casein was 81,585 and 110,000 nmol 32P incorporated/hr/mg of enzyme. Protein kinase N1 comprised one polypeptide of Mr 35,000 which underwent phosphorylation in the presence of Mg2+ + ATP. Protein kinase N2 comprised two polypeptides Mr 40,000 and 30,000 of which only the Mr 30,000 polypeptide was autophosphorylated. Both enzymes were active towards casein, phosvitin, dephosphophosvitin, spermine-binding protein, and non-histone proteins in vitro. Little activity was detected towards histones. Both enzymes were stimulated by 150-200 mM NaCl. MgCl2 requirement varied with the protein substrate but was between 2-4 mM for both enzymes. With dephosphophosvitin as substrate, the apparent Km for ATP for N1 protein kinase was 0.01 mM. GTP did not replace ATP in this reaction. Protein kinase N2 was active in the presence of ATP or GTP. The apparent Km was 0.01 mM for ATP, but 0.1 mM for GTP. 相似文献
17.
S Ansar Ahmed M J Dauphinee N Talal 《Journal of immunology (Baltimore, Md. : 1950)》1985,134(1):204-210
The effects of short-term administration (2 to 4 wk) of sex hormones on the immune system of normal (C57BL/6) and autoimmune (C57BL/6-lpr, C3H/lpr, B/W) strains of mice were investigated. Both estrogen (E2) and testosterone (Te) had significant effects on the numbers of T and B cells as well as on the density of cell surface antigens as demonstrated by flow cytometry. For example, Te depleted Thy-1.2+ thymocytes in normal mice and brought about a shift to lower density cells. Lyt-2+ cells appeared to be the main target cells of hormonal modulation in normal and autoimmune mice. Both sex hormones significantly depleted these cells in the thymus but had differential effects in the peripheral lymphoid organs, particularly in the spleen. In general, E2 depleted Lyt-2+ cells, whereas Te increased or maintained this subpopulation of cells in spleen and lymph nodes. Similarly, the suppressor cell activity and IL 2 production on a per cell basis in E2-treated animals was diminished, whereas Te-treated animals had normal or enhanced activity. The relevance of these findings to differential sex susceptibility in autoimmune diseases is discussed. 相似文献
18.
A new flavone, asplenetin, has been isolated from Launea asplenifolia and characterized as 5,7,3′,4′,5′-pentahydroxy-3-(3-methylbutyl)flavone. Its glycoside, asplenetin 5-O-neohesperidoside, is also reported. 相似文献
19.
The kinetics of the oxidation of CoII(EDTA)2− by IO4− were studied in various ethanol + water mixtures covering the range 7.9 to 58.0 wt% ethanol, at five different temperatures in the range 15–35 °C. The effect of solvent on the rate and mechanism of the reaction was investigated. An inner-sphere mechanism for the reaction was proposed and supported by the calculated activation parameters. 相似文献
20.
Two phosphoglucose isomerases (PGI) with different electrophoretic mobilities have been found in all groups of teleostean fishes studied, with the exception of the Clupeomorpha. PGI proved to be a good taxonomic criterion to differentiate members of the Nemipteridae, Sciaenidae, Platycephalidae and Stromateidae from the other teleost families. 相似文献