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1.
Physical chemical studies of short-chain lecithin homologues. II. Micellar weights of dihexanoyl- and diheptanoyllecithin 总被引:2,自引:0,他引:2
The micellar weights of dihexanoyl- and diheptanoyllecithin in aqueous solutions are calculated from light scattering and ultracentrifugation data. A monomer-micelle assocation model is used and corrections for the thermodynamic nonideality, on the basis of rigid noninteracting particles, are applied. A few experiments on the influence of high NaCI concentrations (up to 3 M) are described. Dihexanoyllecithin forms micelles with micellar weight of 15 000 to 20 000 and with rather narrow weight distributions. Diheptanoyllecithin micelles however, have broad size distributions with micellar weights of 20 000 up to about 100 000 in the concentration range studied. Micelles are assumed to be spherical or to have sphero-cylindrical shapes depending on the molecular weights. Two models are used: (1) a compact structure, where no attention is paid to the hydrocarbon-water contact (2) micelles with as little hydrocarbon-water contact as possible. 相似文献
2.
Synergistic effect of 1-aminocyclopropane-1-carboxylic acid and ethylene during senescence of isolated carnation petals 总被引:2,自引:0,他引:2
The effects of ethylene (C2 H4 ), (2-chloroethyl)phosphonic acid (ethefon) and 1-aminocyclopropane-1-carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers ( Dianthus caryophyllus L. cv. White Sim) were investigated.
Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.
The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC.
In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide. 相似文献
Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.
The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC.
In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide. 相似文献
3.
L. S. van Overbeek J. D. van Elsas J. T. Trevors M. E. Starodub 《Microbial ecology》1990,19(3):239-249
One year after introduction into agricultural drainage waterPseudomonas fluorescens R2f (RP4),Pseudomonas putida CYM318 (pRK2501), andKlebsiella aerogenes NCTC418 (pBR322) could be recovered on agar media. Survival of the introduced strains depended on competition with the indigenous microflora, the presence of nutrients, and the availability of air.In contrast toK. aerogenes NCTC418 (pBR322), bothPseudomonas species lost their plasmids, as indicated by the consistently lower colony counts on selective medium compared with the counts on nonselective medium. The plasmid loss did not depend on nutrient status and oxygen supply.
P. fluorescens R2f cells could be detected with the immunofluorescence (IF) technique. Total cell counts determined by IF were consistently higher than corresponding colony counts. Even in samples where no colonies were recovered, R2f cells could be detected by IF. This indicated the occurrence of nonculturable R2f cells in drainage water. Homology with32P-labelled plasmid RP4 DNA was found in several drainage water samples that originally receivedP. fluorescens R2f (RP4), by using the cell suspension filter hybridization technique.
P. putida CYM318 andK. aerogenes NCTC418 cells could also be detected in sterile drainage water samples, after nonspecific staining with fluorescein isothiocyanate. Cell counts of both strains were consistently higher than corresponding plate counts. 相似文献
4.
The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds. 相似文献
5.
The metabolic pathway collection from EMP: the enzymes and metabolic pathways database. 总被引:4,自引:1,他引:3
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E Selkov S Basmanova T Gaasterland I Goryanin Y Gretchkin N Maltsev V Nenashev R Overbeek E Panyushkina L Pronevitch E Selkov Jr I Yunus 《Nucleic acids research》1996,24(1):26-28
The Enzymes and Metabolic Pathways database (EMP) is an encoding of the contents of over 10 000 original publications on the topics of enzymology and metabolism. This large body of information has been transformed into a queryable database. An extraction of over 1800 pictorial representations of metabolic pathways from this collection is freely available on the World Wide Web. We believe that this collection will play an important role in the interpretation of genetic sequence data, as well as offering a meaningful framework for the integration of many other forms of biological data. 相似文献
6.
B L Maidak G J Olsen N Larsen R Overbeek M J McCaughey C R Woese 《Nucleic acids research》1996,24(1):82-85
The Ribosomal Database Project (RDP) is a curated database that offers ribosome-related data, analysis services and associated computer programs. The offerings include phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams and various software for handling, analyzing and displaying alignments and trees. The data are available via anonymous ftp (rdp.life.uiuc.edu), electronic mail (server@rdp.life.uiuc.edu), gopher (rdpgopher.life.uiuc.edu) and World Wide Web (WWW)(http://rdpwww.life.uiuc.edu/). The electronic mail and WWW servers provide ribosomal probe checking, screening for possible chimeric rRNA sequences, automated alignment and approximate phylogenetic placement of user-submitted sequences on an existing phylogenetic tree. 相似文献
7.
8.
Chlorophyll loss in leaves of cut flowers of alstroemeria (Alstroemeria pelegrina L. cv. Westland) was rapid in darkness and counteracted by irradiation and treatment of the flowers with gibberellic acid (GA3). The mechanism of the effect of GA3 under dark conditions was investigated. The content of various carbohydrates in the leaves under dark conditions rapidly decreased; this was not influenced by treatment with GA3. indicating that the loss of carbohydrates in the leaves did not induce the loss of chlorophyll. Placing the cut flowers in various solutions of organic and inorganic nutrients exhibited no significant effect on the retention of chlorophyll in leaves of dark-senescing flowers. The total nitrogen content in leaves of dark-senescing cut flowers decreased with time. Leaves of GA3-treated flowers retained more nitrogen. In contrast, the buds of GA3-treated flowers retained less nitrogen during senescence in the dark than control buds. To investigate whether GA3 affects export of assimilates from the leaf to various parts of control and GA3-treated flowers, we labelled one leaf with radioactive carbon dioxide. 14C-assimilates accumulated preferentially in the flowers, in which the relative specific activity of the youngest floral buds was highest. No significant differences were observed in the distribution of 14C-labelled compounds between the buds of control and GA3-treated flowers. To establish the importance of source-sink relations for the loss of leaf chlorophyll we removed the flower buds (i. e. the strongest sink) from the cut flowers. This removal only slightly delayed chlorophyll loss as compared to the large delay caused by GA3-treatment. In addition, detached leaf tips exhibited chlorophyll loss in the dark, which was delayed by GA3-treatment in a fashion comparable with that in flowers. Together these data demonstrate that interactions of the leaves with other plant organs are not essential for chlorophyll loss during senescence in the dark. Additionally, we have found no evidence that GA3 delays the loss of chlorophyll by affecting the transport of nutrients within the cut flowers. 相似文献
9.
Contrasting roles for c-Myc and L-Myc in the regulation of cellular growth and differentiation in vivo. 总被引:8,自引:0,他引:8
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S D Morgenbesser N Schreiber-Agus M Bidder K A Mahon P A Overbeek J Horner R A DePinho 《The EMBO journal》1995,14(4):743-756
Although myc family genes are differentially expressed during development, their expression frequently overlaps, suggesting that they may serve both distinct and common biological functions. In addition, alterations in their expression occur at major developmental transitions in many cell lineages. For example, during mouse lens maturation, the growth arrest and differentiation of epithelial cells into lens fiber cells is associated with a decrease in L- and c-myc expression and a reciprocal rise in N-myc levels. To determine whether the down-regulation of L- and c-myc are required for mitotic arrest and/or completion of differentiation and whether these genes have distinct or similar activities in the same cell type, we have studied the consequences of forced L- and c-myc expression in the lens fiber cell compartment using the alpha A-crystallin promoter in transgenic mice (alpha A/L-myc and alpha A/c-myc mice). With respect to morphological and molecular differentiation, alpha A/L-myc lenses were characterized by a severely disorganized lens fiber cell compartment and a significant decrease in the expression of a late-stage differentiation marker (MIP26); in contrast, differentiation appeared to be unaffected in alpha A/c-myc mice. Furthermore, an analysis of proliferation indicated that while alpha A/L-myc fiber cells withdrew properly from the cell cycle, inappropriate cell cycle progression occurred in the lens fiber cell compartment of alpha A/c-myc mice. These observations indicate that continued late-stage expression of L-myc affected differentiation processes directly, rather than indirectly through deregulated growth control, whereas constitutive c-myc expression inhibited proliferative arrest, but did not appear to disturb differentiation. As a direct corollary, our data indicate that L-Myc and c-Myc are involved in distinct physiological processes in the same cell type. 相似文献
10.
Effect of the sequences upstream from the ribosome-binding site on the yield of protein from the cloned gene for phage MS2 coat protein 总被引:14,自引:0,他引:14
The translational efficiency of the coat protein gene of phage MS2 has been examined in vivo with respect to neighbouring sequences. The cloned MS2 DNA has been gradually shortened starting at the 5' or 3' terminus, and its effect on coat protein synthesis monitored. Removal of the 3'-terminal sequences had little influence. In contrast, the gradual removal of the 5'-terminal region profoundly reduces translation. Long before the ribosomal binding site (RBS) of the coat protein (CP) gene is reached, the yield of CP has dropped by one order of magnitude. Functional half-lives of the various messengers were found not to be significantly different. Available evidence indicates that the secondary structure of the RBS in native and shortened MS2 RNA is identical. We infer that important determinants for ribosome recognition lie 5' to the RBS region of the MS2 RNA coat gene. 相似文献