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31.
Recombinant DNA techniques allow any parasite gene to be isolated, propagated and analysed in great detail. The techniques are now well known and widely used in research on parasite diagnosis, vaccine development and identification of chemotherapeutic targets. There are difficulties, for example in analysing carbohydrate antigens, and in selecting which genes merit the intensive investigation required. In this article john Kelly and Mark Blaxter discuss two simple procedures that allow recombinant clones to be characterized rapidly on the basis of both the parasite DNA sequences that they carry and the parasite antigens that they produce. They take examples from work on antigens of Leishmania donovani. 相似文献
32.
Jaroslav Votruba Jarmila Pazlarová Milada Dvořáková Kalju Vanatalu Libuše Váchová Marie Strnadová Helena Kučerová Jiří Chaloupka 《Applied microbiology and biotechnology》1987,26(4):373-377
Summary A mathematical model was formulated to describe the kinetics and stoichiometry of growth and proteinase production in Bacillus megaterium. Synthesis of the extracellular proteinase in a batch culture is repressed by amino acids. The specific rate of formation of the enzyme (r
E) can be described by the formula {ie373-1}, where k
2 and k
3 stand for the non-repressible and repressible part of enzyme synthesis respectively, k
S
2 is a repression coefficient and S
2 indicates the concentration of amono acids; the values of k
2 and k
S
2 depend on the composition of the mixture of amino acids. Even in a high concentration, a single amino acid is less effective than a mixture of amino acids. The dependence of the proteinase repression on the concentration of an external amino acid (leucine) follows the same course as its rate of incorporation into proteins, approaching saturation at concentrations higher than 50 M (half saturation approximately 10 M). However, the total uptake of leucine did not exhibit any saturation even at 500 M external concentration.Symbols
X
biomass concentration, g/l
-
E
proteinase concentration, unit/l
-
t
time, h
-
S
1
concentration of glucose, g/l
-
S
2
concentration of amino acids, g/l
-
specific growth rate, l/h
-
rE
specific rate of enzyme production, unit/g/h
-
k
1
growth kinetic constant, l/h
-
k
2
product formation kinetic constant (for non-repressible part of enzyme synthesis), unit/g
-
k
3
product formation kinetic constant (for repressible portion of enzyme synthesis), unit/g
-
k
S
1
saturation constant, g/l
-
k
S
2
repression coefficient for a certain amino acid or amino acids mixture, g/l 相似文献
33.
Postnatal D2-CAM/N-CAM Sialylation State Is Controlled by a Developmentally Regulated Golgi Sialyltransferase 总被引:2,自引:0,他引:2
Abstract: Golgi-enriched fractions have been isolated from rat brain of increasing postnatal age and defined by electron microscopy and distribution of marker enzymes. The expression of sialyltransferase activity associated with these fractions has been demonstrated to developmentally decrease and this appeared to be, in part, dependent on endogenous competitive inhibition. The developmental regulation of this activity paralleled the sialylation state of the neural cell adhesion molecule (D2-CAM/N-CAM) and could be demonstrated to be capable of endogenously sialylating this protein in the isolated Golgi fractions. In 12-day-old animals the majority of the transferred [14 C]sialic acid was found to be associated with the high-molecular-weight [>200 kilodaltons (kd)] form of D2-CAM/N-CAM, indicative of the protein having been heavily sialylated. Sialylation of the individual D2-CAM/N-CAM polypeptides was also demonstrated in both 12-day and adult animals and transfer was evident only in the 180-kd and 115-kd components and not in the 140-kd component. In contrast, Golgi-enriched fractions prepared from adult animals showed little capability of heavily sialylating D2-CAM/N-CAM to any significant extent. 相似文献
34.
G Jahn I Dusanter-Fourt P A Kelly L M Houdebine J Djiane 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1987,184(1):19-23
A specific homologous radioimmunoassay was developed to measure rabbit beta-casein in rabbit mammary gland with a sensitivity of 0.5 ng/ml protein. It was used to measure casein concentration during pregnancy and in organ culture of mammary gland explants. Casein was detectable in virgin mammary glands, showed a small increase during the first half of pregnancy, increased more than 20-fold between Days 21 and 27, and diminished somewhat on the first days of lactation. After 24 hr of culture, mammary gland explants had no detectable casein, but the addition of increasing concentrations of prolactin to a culture medium which contained insulin (5 micrograms/ml) and cortisol (0.5 microgram/ml) induced a regular increase in the casein content of the tissue. Casein started to increase when 10 ng/ml of prolactin was present and maximal values were achieved for 100 ng/ml of the hormone. 相似文献
35.
Carlos Eduardo Falavigna da Rocha Maria Helena Gonzaga de Carvalho Bjornber 《Hydrobiologia》1987,153(2):97-107
Cyclopid copepods collected mainly in aquatic microcosms and semiterrestrial habitats in the Juréia Ecological Reserve are studied. Hesperocyclops herbsti and Bryocyclops campaneri are described as new species and their taxonomical relationships discussed. Females of Muscocyclops operculatus (Chappuis) are redescribed and the males described for the first time. An emended diagnosis for Muscocyclops is proposed. 相似文献
36.
The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Müller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Müller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna.
Animal Ecology Research Group, Department of Zoology, University of Oxford
Commonwealth Forestry Institute, Department of Plant Sciences, University of Oxford 相似文献
37.
In vitro mutagenesis of trypsinogen: role of the amino terminus in intracellular protein targeting to secretory granules 总被引:8,自引:6,他引:2
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The mouse anterior pituitary tumor cell line, AtT-20, targets secretory proteins into two distinct intracellular pathways. When the DNA that encodes trypsinogen is introduced into AtT-20 cells, the protein is sorted into the regulated secretory pathway as efficiently as the endogenous peptide hormone ACTH. In this study we have used double-label immunoelectron microscopy to demonstrate that trypsinogen colocalizes in the same secretory granules as ACTH. In vitro mutagenesis was used to test whether the information for targeting trypsinogen to the secretory granules resides at the amino (NH2) terminus of the protein. Mutations were made in the DNA that encodes trypsinogen, and the mutant proteins were expressed in AtT-20 cells to determine whether intracellular targeting could be altered. Replacing the trypsinogen signal peptide with that of the kappa-immunoglobulin light chain, a constitutively secreted protein, does not alter targeting to the regulated secretory pathway. In addition, deletion of the NH2-terminal "pro" sequence of trypsinogen has virtually no effect on protein targeting. However, this deletion does affect the signal peptidase cleavage site, and as a result the enzymatic activity of the truncated trypsin protein is abolished. We conclude that neither the signal peptide nor the 12 NH2-terminal amino acids of trypsinogen are essential for sorting to the regulated secretory pathway of AtT-20 cells. 相似文献
38.
The relationship between pressure and temperature as it affects microbial growth and metabolism has been examined only for a limited number of bacterial species. Because many newly-discovered, extremely thermophilic bacteria have been isolated from pressurized environments, this relationship merits closer scrutiny. In this study, the extremely thermophilic bacterium, Sulfolobus acidocaldarius, was cultured successfully in a hyperbaric chamber containing helium and air enriched with 5% carbon dioxide. Over a pressure range of approximately 1-120 bar and a temperature range of 67-80 degrees C, growth was achieved in a heterotrophic medium with the air mixture at partial pressures up to 3.5 bar. Helium was used to obtain the final, desired incubation pressure. No significant growth was noted above 80 degrees C over the same range of hyperbaric pressures, or at 70 degrees C when pressure was applied hydrostatically. Growth experiments conducted under hyperbaric conditions may provide a means to study these bacteria under simulated in situ conditions and simultaneously avoid the complications associated with hydrostatic experiments. Results indicate that hyperbaric helium bioreactors will be important in the study of extremely thermophilic bacteria that are isolated from pressurized environments. 相似文献
39.
Helena Lennholm Bengt Lindberg Ulf Lindquist Frank Lindh Bo Nilsson 《Glycoconjugate journal》1987,4(4):313-316
N-Deacetylation of 2-acetamido-2-deoxy-hexose residues is accomplished in liquid ammonia containing calcium. Oligosaccharides, lacto-N-fucopentaose II and lacto-N-difucohexaose I, containing 3,4-disubstitutedN-acetylhexosamine residues are quantitativelyN-deacetylated. When applied to polysaccharides, however, only partialN-deacetylation was achieved.Author for correspondence. AXRD 相似文献