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11.
Solid-phase synthesis of peptides was carried out using only the volume of the solvent included in the swollen solid-phase resin beads [inclusion volume synthesis]. This approach enables (i) the use of higher concentrations of activated amino acids, resulting in increased coupling rates, (ii) drastically decreased consumption of solvents, and (iii) the construction of multiple peptide synthesizers having virtually no reaction vessels. 相似文献
12.
I. Michalík 《Biologia Plantarum》1982,24(3):161-169
In an experiment with native maize roots depending on different phosphorus concentration in the external solution (0.001 …
50 mM P), the multiphasic character of the kinetics of phosphate uptake has been stated. The single phases are characterized
by the different values of Km and Vmax. In the wide range of concentrations the isotherm of the phosphate uptake has five evident phases. The character of kinetics
for the uptake of phosphate is analogical to the kinetics of the enzymatic reactions described by the Michaelis-Menten equation.
On the other hand the linear dependence for the inactivated root was determined,i.e. the uptake of phosphate versus different phosphorus concentration in the external solution.
The graphic representation of the logarithmic values for the phosphorus taken up versus the different phosphorus concentration
in the external solution gives the biphasic course including concentration less than 1.0 mM P and more than 1.0 mM P. Within
the framework of the concentration range the following values of Vmax, Km and ϕin were calculated under the conditions if the concentration of phosphorus is less than 1.0mMP: Vmax = 1.705 μmol P × g-1h-1, Km = 0.057 mM P and ϕin = 0.83,i.e. if the concentration of phosphorus is more than 1.0mM P: Vmax = 40 μmol P × g-1 h-1, Km = 16.66 mM and ϕin = 20.
According to these results, the phosphate concentration in the external solution influences the activity of the transport
mechanisms concerning their conformative changes which discretely change their working regime of membrane transport. This
is also demonstrated in the change of values Vmax, Km and ϕin. 相似文献
13.
Michal Pop 《Hydrobiologia》1991,225(1):169-176
The changes of selected parameters of the filtering comb of the third thoracic limb were studied in a natural population of Daphnia pulicaria Forbes, as well as in experimental enclosures and in lab cultures, including individual life history. Two hypotheses were tested: 1. either these changes are related to the succession of clones coexisting within one population, or 2. the size of the filtering area changes gradually as an individual adaptation during the moulting. No evidence supporting the clonal hypothesis was found. On the contrary, the adaptability of the filtering comb is the same in a natural population as it is in a clone and in individuals. 相似文献
14.
Human retinal vascular cells differ from umbilical cells in synthetic functions and their response to glucose. 总被引:4,自引:0,他引:4
Z Rymaszewski P T Szymanski W A Abplanalp L Myatt J Di Salvo R M Cohen 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1992,199(2):183-191
Cell culture systems have commonly been used to study mechanisms implicated in the pathogenesis of diabetic retinopathy, but the great majority of cell preparations used have been either of nonhuman retinal origin or nonretinal human origin. Because of questions of species and organ specificity in the function of cells of vascular origin, in this study, cultured microvascular endothelial cells (HREC), pericytes (HRPC), and pigment epithelial cells from the postmortem human retina, and endothelial cells from human umbilical vein (HUVEC) were evaluated with respect to cell proliferation, and secretory products potentially important in diabetic retinopathy, i.e., prostaglandins (PG) and plasminogen activators (PA), normalized to DNA content/well, under both basal (5 mM) and high (25 mM) glucose conditions. Glucose (25 mM) reduced DNA content similarly in both types of endothelial cells, had a lesser effect on HRPC, and did not significantly alter the proliferation of pigment epithelial cells. Basal secretion of PGI2 (measured as 6-keto-PGF1 alpha) was in the order HRPC much greater than HREC greater than HUVEC, whereas PGE2 secretion was in the order HREC much greater than HRPC greater than HUVEC. Glucose (25 mM) stimulated PGI2 secretion by HRPC, but not by either type of endothelial cell, and enhanced PGE2 secretion by HREC, but not by HUVEC or HRPC. Release of plasminogen activator activity differed between HUVEC and HREC under basal conditions and addition of 25 mM glucose stimulated release only from HREC. Glucose (25 mM) stimulated PA secretion by HREC, but not by HUVEC. These findings provide evidence that human retinal pericytes are an important source of prostacyclin, and that there are differences between HREC and HUVEC with respect to secretory functions and their modulation by glucose, indicating regional specificity of these functions. Extrapolation to human retinal vascular cells from experiments using cells from heterologous vascular beds to draw inferences about the pathophysiology of diabetic retinopathy are not valid for these cellular functions. 相似文献
15.
Construction and properties of K1 type killer wine yeasts 总被引:3,自引:0,他引:3
Summary With the use of a protoplast fusion technique the killer character of K1 type was transferred into four industrial Saccharomyces wine yeasts. The prototrophic yeast strains active against standard sensitive and K2 killer Saccharomyces strains, resistant to K1 killer toxin were constructed with no changes in technological properties. 相似文献
16.
17.
Accelerated uptake of 5-hydroxytryptamine by human blood platelets enriched in a sialic acid. 下载免费PDF全文
The enzymically catalysed incorporation of N-acetylneuraminic acid into human platelets, whether suspended in their own citrated plasma or in buffered saline containing 0.17 mM-sucrose, accelerated the uptake of 5-hydroxytryptamine. This acceleration decreased with time. The observations may be explained by assuming that N-acetylneuraminic acid is a component of a transport receptor for 5-hydroxytryptamine. 相似文献
18.
19.
Genetic Variability within Borrelia burgdorferi Sensu Lato Genospecies Established by PCR-Single-Strand Conformation Polymorphism Analysis of the rrfA-rrlB Intergenic Spacer in Ixodes ricinus Ticks from the Czech Republic 总被引:1,自引:0,他引:1 下载免费PDF全文
Markta Derdkov Lorenza Beati Branislav Pet'ko Michal Stanko Durland Fish 《Applied microbiology》2003,69(1):509-516
In Europe the Borrelia burgdorferi sensu lato complex is represented by five distinct genospecies: Borrelia burgdorferi sensu stricto, Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, and Borrelia lusitaniae. These taxonomic entities are known to differ in their specific associations with vertebrate hosts and to provoke distinct clinical manifestations in human patients. However, exceptions to these rules have often been observed, indicating that strains belonging to a single genospecies may be more heterogeneous than expected. It is, therefore, important to develop alternative identification tools which are able to distinguish Borrelia strains not only at the specific level but also at the intraspecific level. DNA from a sample of 370 Ixodes ricinus ticks collected in the Czech Republic was analyzed by PCR for the presence of a ~230-bp fragment of the rrfA-rrlB intergenic spacer of Borrelia spp. A total of 20.5% of the ticks were found to be positive. The infecting genospecies were identified by analyzing the amplified products by the restriction fragment length polymorphism (RFLP) method with restriction enzyme MseI and by single-strand conformation polymorphism (SSCP) analysis. The two methods were compared, and PCR-SSCP analysis appeared to be a valuable tool for rapid identification of spirochetes at the intraspecific level, particularly when large samples are examined. Furthermore, by using PCR-SSCP analysis we identified a previously unknown Borrelia genotype, genotype I-77, which would have gone unnoticed if RFLP analysis alone had been used. 相似文献
20.
Alonso Adel C Mederlyova A Novak M Grundke-Iqbal I Iqbal K 《The Journal of biological chemistry》2004,279(33):34873-34881
Mutations in the tau gene are known to cosegregate with the disease in frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). However, the molecular mechanism by which these mutations might lead to the disease is not understood. Here, we show that four of the FTDP-17 tau mutations, R406W, V337M, G272V, and P301L, result in tau proteins that are more favorable substrates for phosphorylation by brain protein kinases than the wild-type, largest four-repeat protein tau4L and tau4L more than tau3L. In general, at all the sites studied, mutant tau proteins were phosphorylated faster and to a higher extent than tau4L and tau4L > tau3L. The most dramatic difference found was in the rate and level of phosphorylation of tau4L(R406W) at positions Ser-396, Ser-400, Thr-403, and Ser-404. Phosphorylation of this mutant tau was 12 times faster and 400% greater at Ser-396 and less than 30% at Ser-400, Thr-403, and Ser-404 than phosphorylation of tau4L. The mutated tau proteins polymerized into filaments when 4-6 mol of phosphate per mol of tau were incorporated, whereas wild-type tau required approximately 10 mol of phosphate per mol of protein to self-assemble. Mutated and wild-type tau proteins were able to sequester normal tau upon incorporation of approximately 4 mol of phosphate per mol of protein, which was achieved at as early as 30 min of phosphorylation in the case of mutant tau proteins. These findings taken together suggest that the mutations in tau might cause neurodegeneration by making the protein a more favorable substrate for hyperphosphorylation. 相似文献