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1.
M. A. P. J. Hacking F. van Rantwijk R. A. Sheldon 《Journal of Molecular Catalysis .B, Enzymatic》2000,9(4-6):201-208
Symmetrical dialkyl carbonates and dibenzyl carbonates reacted with various nucleophiles in the presence of Candida antarctica lipase B in organic solvents. For example, reaction of dibutyl and dibenzyl carbonate with an alcohol gave a mixture of the mono- and disubstituted products. Aminolysis, however, afforded only the carbamates, without subsequent reaction to the ureum derivatives. The reaction rates were rather low compared with carboxylic esters; the reactivity increased in the order dimethyl相似文献
2.
《Biocatalysis and Biotransformation》2013,31(2):127-134
The fatty acid specificity of the B-lipase derived from Candida antarctica was investigated in the synthesis of esters of ethyl D-glucopyranoside. The specificity was almost identical with respect to straight-chain fatty acids with 10 to 18 carbon atoms. However, lower fatty acids such as hexanoic and octanoic acid and the unsaturated 9-cis-octadecenoic acid were found to be poor substrates of the enzyme. As a consequence of this selectivity, these fatty acids were accumulated in the unconverted fraction when ethyl D-glucopyranoside was esterified with an excess of a mixture of fatty acids. This accumulation can reduce the overall effectiveness of the process as the activity of the lipase was found to be reduced when exposed to high concentrations of short-chain fatty acids. Finally, using a simplified experimental set-up, the specificity of the C. antarctica B-lipase was compared to the specificity of lipases derived from C. rugosa, Mucor miehei, Humicola, and Pseudomonas. Apart from the C. rugosa lipase, which exhibited a very poor performance, all the enzymes showed a very similar specificity with respect to fatty acids longer than octanoic acid while only the C. antarctica B-lipase showed activity towards sort-chain fatty acids. 相似文献
3.
Ursula J. Behrens Fiorenzo Paronetto 《In vitro cellular & developmental biology. Plant》1984,20(5):391-395
Summary In our laboratory, airborne yeast contaminants of cell cultures have consistently been of the genusCandida (speciesCandida parapsilosis), which are difficult to control with fungicidal agents. To salvage cell lines that show the presence of this fungus, two
effective methods may be employed. In early stages of infection, the addition of activated mouse peritoneal macrophages (5×105 cells/ml) to the culture medium containing 5 μg Fungizone/ml eliminates all spores by phagocytosis. More heavily contaminated
cultures can be depleted of fungi by density centrifugation on a layer of 38% Percoll. Remaining single spores, often not
detectable by light microscopy, can be removed by the addition of macrophages (2×105/ml) and Fungizone (5 μg/ml) to the culture medium. Contaminated monolayer cells can be freed of blastospores by several washes
with balanced salt solution and subsequent culturing for 4 d in medium containing 10 μg Fungizone/ml without any toxic effects
to the cells. These procedures can rescue valuable cell lines and hybridomas that would otherwise be lost.
This work was supported by Veterans Administration Research Funds. 相似文献
4.
Abstract The kinetic parameters of NH+ 4 -uptake in yeast cells were determined by a method that is based on the following changes in the external NH+ 4 concentration in cell suspensions by using NADH-dependent glutamate formation from NH+ 4 and 2-oxoglutarate. The kinetics of the observed NADH oxidation were analyzed by computer and enabled an estimation of V max and K m of the NH+ 4 -uptake system of the cells. 相似文献
5.
Tadayo Hashimoto 《Journal of microbiological methods》1983,1(2):89-98
A micromethod for the quantitative determination of the viability of Candida albicans hypae was devised which takes advantage of the dimorphic nature of C. albicans which grows exclusively in the yeast form when incubated aerobically on Sabouraud dextrose agar at 30°C. When tested by thisd method, all viable, C. albicans hyphae were recognized as microcolonies consisting of one hypha surrounded by several yeast form progeny. In contrast to this, no yeast form progeny emerged from nonviable hypae. By counting appropriate total numbers (200–400) of microcolony-forming hypae and infertile hyphae, it was possible to determine the ratio of viable to nonviable cells in a given hyphal suspension. This micromethod may be used for quantitative assessment of the candidacidal effects of various antimycotic agents or phagocytes C. albicans hyphae whose viability could not have been determined by the conventional plating technique because of the species' high propensity to clump. 相似文献
6.
Candida albicans secretes both hydroxamate and phenolate-type siderophores when grown under iron-restricted conditions. The inhibition of candidal growth by iron limitation was reversed by the addition of supplemental hydroxamate on phenolate siderophores. Both siderophores produced equal stimulation of growth suggesting that C. albicans could utilize both siderophores with equal efficiency. Addition of heterologous siderophores from both bacteria and fungi also supported growth of the yeast in a deferrated medium. These results suggest that C. albicans has an iron-uptake mechanism which enables it to obtain iron by utilizing candidal and non-candidal siderophores. 相似文献
7.
Abstract Transport of Mn2+ was repressed in Candida utilis cells grown in continuous culture in high-Mn2+ (100 μM Mn2+ ) medium as compared to cells grown in basic (0.45 μM Mn2+ ) and low-Mn2+ (< 0.05 μM Mn2+ ) media. In contrast, no repression of Cu2+ uptake occurred in high-Cu2+ -grown (25 μM Cu2+ ) cells as compared to cells grown in basic medium (0.54 μM Cu2+ ). Cu2+ -limited cells did not hyperaccumulate Cu2+ and there was not significant difference in initial uptake rates for all 3 Cu2+ conditions. Mn2+ uptake appears to be regulated by a mechanism sensitive to the external Mn2+ concentration, whereas Cu2+ transport is not governed in this way by the external Cu2+ . 相似文献
8.
Efficient preparation of spheroplasts fromCandida utilis, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, using a purified mixture of enzymes fromTrichoderma harzianum, is described. Limitations of other methods, and differences between yeasts are demonstrated. 相似文献
9.
One-step gene disruption by cotransformation to isolate double auxotrophs in Candida albicans 总被引:11,自引:0,他引:11
Summary The Candida albicans LEU2 gene was disrupted by substituting lambda DNA for a small deletion within the LEU2 gene. Cotransformation with a selectable URA3 ARS vector was used to introduce a linear fragment containing the disruption into the genome of a C. albicans ura3 deletion mutant. Cotransformants containing the lambda DNA were identified by colony hybridization and the URA3 plasmid was subsequently cured. Leu2 disrupted heterozygotes were detected by Southern hybridization and one disruptant was subsequently treated with UV irradiation. Only one leu2 ura3 mutant (SGY-484) was isolated out of 11,000 mutagenized cells. SGY-484 was transformed to Leu+ with either the C. albicans or Saccharomyces cerevisiae LEU2 gene. Southern hybridization analysis revealed that the mutant is not homozygous for the disruption; the leu2 mutation reverts and is most likely a point mutation. Unexpectedly, an ade2 ura3 mutant was isolated from the same mutagenesis. 相似文献
10.
To assess the dynamics of synthesis of the wall by regenerating Candida albicans protoplasts deposition of chitin and mannoproteins were investigated ultrastructurally using wheat germ agglutinin conjugated with either horseradish peroxidase or colloidal gold, and Concanavalin A coupled to ferritin respectively.Freshly prepared protoplasts lacked wheat germ agglutinin receptor sites but after 1–2 h of regeneration, they were detected. After 4–5 h of regeneration, the cell wall showed a discrete structure which was only labelled with wheat germ agglutinin in thin sections. At this stage of regeneration the outermost layer of the wall was labelled with clusters of Concanavalin A-ferritin particles.After 8 h regeneration, the cell wall appeared compact, and homogenously marked with wheat germ agglutinin whereas only the surface layers appeared consistently labelled with Concanavalin A-ferritin.From these observations we conclude that C. albicans protoplasts are able to regenerate in liquid medium a cell wall consisting of a network of chitin fibrils and mannoproteins at least (glucan polymers were not determined in the present cytological study). The former are the fundamental component of the inner layers at early stages of regeneration, whereas the latter molecules are predominant in the outer layers of the wall.Abbreviations WGA-HRP
wheat germ agglutinin conjugated with horseradish peroxidase
- WGA-Au
wheat germ agglutinin conjugated with colloidal gold
- Con A-ferritin
Concanavalin A coupled to ferritin 相似文献