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1.
2.
High level of divergence of male-reproductive-tract proteins, between Drosophila melanogaster and its sibling species, D. simulans 总被引:1,自引:0,他引:1
We compared male-reproductive-tract polypeptides of Drosophila melanogaster
and D. simulans by using two-dimensional gel electrophoresis. Approximately
64% of male-reproductive-tract polypeptides were identical between two
randomly chosen isofemale lines from these two species, compared with 83%
identity for third-instar imaginal wing-disc polypeptides. Qualitatively
similar differences were found between reproductive tracts and imaginal
discs when D. sechellia was compared with D. melanogaster and with D.
simulans. When genic polymorphism was taken into account, approximately 10%
of male- reproductive-tract polypeptides were apparently fixed for
different alleles between D. melanogaster and D. simulans; this proportion
is the same as that found for soluble enzymes by one-dimensional gel
electrophoresis. Strikingly, approximately 20% of male-reproductive- tract
polypeptides of either D. melanogaster or D. simulans had no detectable
homologue in the other species. We propose that proteins of the Drosophila
male reproductive tract may have diverged more extensively between species
than have other types of proteins and that much of this divergence may
involve large changes in levels of polypeptide expression.
相似文献
3.
Trypanothione reductase of Trypanosoma congolense: gene isolation, primary sequence determination, and comparison to glutathione reductase 总被引:6,自引:0,他引:6
The gene encoding trypanothione reductase, the redox disulfide-containing flavoenzyme that is unique to the parasitic trypanosomatids (Shames et al., 1986), has been isolated from the cattle pathogen Trypanosoma congolense. Library screening was carried out with inosine-containing oligonucleotide probes encoding sequences determined from two active site peptides isolated from the purified Crithidia fasciculata enzyme. The nucleotide sequence of the gene was determined according to the dideoxy chain termination method of Sanger. The structural gene is 1476 nucleotides long and encodes 492 amino acids. We have identified the active site peptide containing the redox-active disulfide, a peptide corresponding to the histidine-467 region of human erythrocyte glutathione reductase, as well as the flavin binding domain that is highly conserved in all disulfide-containing flavoprotein reductase enzymes. Alignment of five tryptic peptides (80 residues) isolated from the C. fasciculata trypanothione reductase with the primary sequence of the T. congolense enzyme showed 88% homology with 76% identity. Additionally, a sequence comparison of the glutathione reductase from Escherichia coli or human erythrocytes to T. congolense trypanothione reductase reveals greater than 50% homology. A search for the amino acid residues in the primary sequence of trypanothione reductase functionally active in binding/catalysis in human erythrocyte glutathione reductase shows that only the two arginine residues (Arg-37 and Arg-347), shown by X-ray crystallographic data to hydrogen bond to the GS1 glutathione glycyl carboxylate, are absent. 相似文献
4.
Nitrogen Nutrition and Xylem Sap Composition of Peanut (Arachis hypogaea L. cv Virginia Bunch) 下载免费PDF全文
The principal forms of amino nitrogen transported in xylem were studied in nodulated and non-nodulated peanut (Arachis hypogaea L.). In symbiotic plants, asparagine and the nonprotein amino acid, 4-methyleneglutamine, were identified as the major components of xylem exudate collected from root systems decapitated below the lowest nodule or above the nodulated zone. Sap bleeding from detached nodules carried 80% of its nitrogen as asparagine and less than 1% as 4-methyleneglutamine. Pulse-feeding nodulated roots with 15N2 gas showed asparagine to be the principal nitrogen product exported from N2-fixing nodules. Maintaining root systems in an N2-deficient (argon:oxygen, 80:20, v/v) atmosphere for 3 days greatly depleted asparagine levels in nodules. 4-Methyleneglutamine represented 73% of the total amino nitrogen in the xylem sap of non-nodulated plants grown on nitrogen-free nutrients, but relative levels of this compound decreased and asparagine increased when nitrate was supplied. The presence of 4-methyleneglutamine in xylem exudate did not appear to be associated with either N2 fixation or nitrate assimilation, and an origin from cotyledon nitrogen was suggested from study of changes in amount of the compound in tissue amino acid pools and in root bleeding xylem sap following germination. Changes in xylem sap composition were studied in nodulated plants receiving a range of levels of 15N-nitrate, and a 15N dilution technique was used to determine the proportions of accumulated plant nitrogen derived from N2 or fed nitrate. The abundance of asparagine in xylem sap and the ratio of asparagine:nitrate fell, while the ratio of nitrate:total amino acid rose as plants derived less of their organic nitrogen from N2. Assays based on xylem sap composition are suggested as a means of determining the relative extents to which N2 and nitrate are being used in peanuts. 相似文献
5.
Enhancement of NMDA-mediated responses by cyanide 总被引:2,自引:0,他引:2
Manisha N. Patel Robert W. Peoples George K. W. Yim Gary E. Isom 《Neurochemical research》1994,19(10):1319-1323
The effect of cyanide on NMDA-activated ion current and MK801 binding was studied in cultured rat hippocampal neurons. In microfluorometric analysis using fura-2, removal of extracellular Mg2+ resulted in a five-fold increase in NMDA-induced peak of [Ca2+]i. One mM NaCN enhanced the peak NMDA responses in the presence, but not in the absence of extracellular Mg2+. Cyanide enhanced the immediate rise in [Ca2+]i produced by NMDA, followed over a 1–5 min period by a gradual increase of [Ca2+]i. Similar results were obtained in whole-cell patch clamp recordings from hippocampal neurons. One mM KCN enhanced the NMDA-activated current in the presence, but not in the absence of extracellular Mg2+. This effect was independent of cyanide-mediated metabolic inhibition since the recording pipette contained ATP (2 mM). In binding assays NaCN (1 mM) increased the binding affinity of [3H]MK-801 to rat forebrain membranes in the presence of Mg2+, whereas in the absence of Mg2+, NaCN did not influence binding. These results indicate that cyanide enhances NMDA-mediated Ca2+ influx and inward current by interacting with the Mg2+ block of the NMDA receptor. The effect of cyanide can be explained by an initial interaction with the Mg2+ block of the NMDA receptor/ionophore which appears to be energy-independent, followed by a gradual increase in Ca2+ influx resulting from cellular energy reserve depletion.Abbreviations NMDA
N-Methyl-D-Aspartate
- EAA
excitatory amino acid
- MK-801
(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohept-5,10-imine maleate 相似文献
6.
Biological nitrogen fixation: An efficient source of nitrogen for sustainable agricultural production? 总被引:26,自引:2,他引:24
A fundamental shift has taken place in agricultural research and world food production. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive, and to be sustainable in the long-term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. In the case of nitrogen (N), inputs into agricultural systems may be in the form of N-fertilizer, or be derived from atmospheric N2 via biological N2 fixation (BNF).Although BNF has long been a component of many farming systems throughout the world, its importance as a primary source of N for agriculture has diminished in recent decades as increasing amounts of fertilizer-N are used for the production of food and cash crops. However, international emphasis on environmentally sustainable development with the use of renewable resources is likely to focus attention on the potential role of BNF in supplying N for agriculture. This paper documents inputs of N via symbiotic N2 fixation measured in experimental plots and in farmers' fields in tropical and temperate regions. It considers contributions of fixed N from legumes (crop, pasture, green manures and trees), Casuarina, and Azolla, and compares the relative utilization of N derived from these sources with fertilizer N. 相似文献
7.
Spontaneous Phloem bleeding from cryopunctured fruits of a ureide-producing legume 总被引:4,自引:4,他引:0 下载免费PDF全文
The vasculature of the dorsal suture of cowpea (Vigna unguiculata [L.] Walp) fruits bled a sugar-rich exudate when punctured with a fine needle previously cooled in liquid N2. Bleeding continued for many days at rates equivalent to 10% of the estimated current sugar intake of the fruit. A phloem origin for the exudate was suggested from its high levels (0.4-0.8 millimoles per milliliter) of sugar (98% of this as sucrose) and its high K+ content and high ratio of Mg2+ to Ca2+. Fruit cryopuncture sap became labeled with 14C following feeding of [14C]urea to leaves or adjacent walls of the fruit, of 14CO2 to the pod gas space, and of [14C] asparagine or [14C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of 14C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of 14C distribution in phloem sap suggested that [14C]allantoin was metabolized to a greater extent in its passage to the fruit than was [14C] asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO3-fed, non-nodulated plants were 20:2:78 in root bleeding xylem sap versus 90:10:0.1 for fruit phloem sap, suggesting that the shoot utilized NO3-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of 15NO3 to roots substantiated this conclusion. The amino acid:ureide ratio (nitrogen weight basis) of root xylem sap of symbiotic plants was 23:77 versus 89:11 for corresponding fruit phloem sap indicating intense metabolic transfer of ureide-nitrogen to amino acids by vegetative parts of the plant. 相似文献
8.
In crude extracts from the primary leaf of wheat seedlings, Triticum aestivum L., cv. Olympic, maximum proteinase activity, as determined by measuring the rate of release of amino nitrogen from ribulose-bisphosphate carboxylase (RuBPCase), was found to be obtained only when EDTA and L-cysteine were included in the extraction buffer. Highest proteinase activity was obtained by grinding at pH 6.8, although the level of activity was similar in the pH range 5.6 to 8.0; this range also coincided with maximum extractability of protein. The lower amount of RuBPCase degrading proteinase extracted at low pH was not due to an effect of pH on enzyme stability. The optimum temperature of reaction was 50° C and reaction rates were linear for at least 120 min at this temperature. In the absence of substrate the proteinase was found to be very sensitive to temperatures above 30° C, with even short exposures causing rapid loss of activity. The relation between assay pH and RuBPCase degradation indicated that degradation was restricted to the acid proteinase group of enzymes, with a pH optimum of 4.8, and no detectable activity at a pH greater than 6.4. The levels of extractable RuBPCase proteinase exhibited a distinct diurnal variation, with activity increasing during the latter part of the light period and then declining once the lights were turned off. The effect of leaf age on the level of RuBPCase, RuBPCase proteinase and total soluble protein was investigated. Maximum RuBPCase activity occurred 9 days after sowing as did soluble protein. After the maximum level was obtained, the pattern of total soluble protein was shown to be characterised by three distinct periods of protein loss: I (day 9–13) 125 ng leaf-1 day-1; II (day 15–27) 11 ng leaf-1 day-1; III (day 29–49) 22 ng leaf-1 day-1. Comparison of the pattern of RuBPCase activity and total protein suggest that the loss of RuBPCase may be largely responsible for the high rate of protein loss during period I. Proteinase activity increased sharply during the period of most rapid loss of RuBPCase activity, and because the specific activity of RuBPCase also declined, we concluded that RuBPCase was being degraded more rapidly than the other proteins. Once the majority of the RuBPCase was lost, there did not appear to be a direct relation between RuBPCase proteinase activity and rate of total soluble protein loss, since the proteinase exhibited maximum activity during the slowest period of protein loss (II), and was declining in activity while the rate of protein loss remained stable during the third and final period of total protein loss.Abbreviations RuBPCase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
- TCA
trichloroacetic acid
Supported by the Wheat Industry Research Council of Australia and the Australian Research Grants Committee D2 74/15052 相似文献
9.
A double blind study was undertaken to determine the effectiveness or oral prostaglandin E2 as a means of improving the pelvic score prior to induction of labour. 48 patients who were greater than 37 were gestation and who had Bishop scores of less than 6 entered the study. Ten tablets were given on an hourly regime. Of 25 patients in the prostaglandin group, 17 were considered successes (68.0%), whereas of 23 patients who received a placebo, 9 were successes (39.1%). No adverse effects were recorded. Prostaglandin E2 is therefore considered a safe and effective method for priming the unfavourable cervix prior to induction of labour. 相似文献
10.
Cytochrome P-448 (mol wt 55,000 Daltons) from rabbit liver was purified to a specific content of 16.6 nmol/mg. Mice were immunised with this preparation, their spleens removed and dissociated lymphocytes hybridised with myeloma cells. Four monoclonal antibodies against cytochrome P-448 were raised and partially characterised. All four antibodies interacted with cytochrome P-448 in intact microsomal fractions and selectively immunoadsorbed cytochrome P-448 from solubilised microsomal preparations. One of the antibodies inhibited benzo[a] pyrene hydroxylase activity in a reconstituted system, one had no effect on activity and two increased activity. The possible applications of such antibodies are discussed. 相似文献