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Biomedical subjects

A Fiechter

Publications and source records attributed to A Fiechter.

At least 73 records · Page 4Linked to original sources
PubMed1986

Effect of mitochondrial cytochromes and haem content on cytochrome P450 in Saccharomyces cerevisiae.

It is well established that the mitochondrial and the microsomal cytochromes in Saccharomyces cerevisiae are regulated differently. Mutations affecting the mitochondrial cytochromes aa3 or c had no effect on the concentration of the microsomal cytochrome P450 even during haem limitation. Moreover, a defect in the cytochrome P450 gene did not affect mitochondrial cytochromes. However, a regulatory mutation present in strain SG1 decreased both mitochondrial and microsomal cytochrome contents. This mutation also affected the intracellular haem concentration. The haem precursor 5-aminolaevulinate increased both mitochondrial and microsomal cytochrome contents. Our results indicate that carbon source and haem concentration are involved in the regulation of cytochrome P450.

Aminolevulinic Acid↗
PubMed1986

Pilot plant production of rhamnolipid biosurfactant by Pseudomonas aeruginosa.

Rhamnolipid biosurfactants were continuously produced with Pseudomonas aeruginosa on the pilot plant scale. Production and downstream processing elaborated on the laboratory scale were adapted to the larger scale. Differences in performance resulting from the scale-up are discussed. A biosurfactant concentration of approximately 2.25 g liter-1 was achieved. The biosurfactant yield on glucose was 77 mg g-1 h-1, and the productivity was 147 mg liter-1 h-1, corresponding to a daily production of 80 g of biosurfactant. The first enrichment step consisted of an adsorption chromatography which was followed by an anion-exchange chromatography. The resulting product was 90% pure, and the overall recovery of active material was above 60% with the downstream processing used.

Centrifugation↗
PubMed1985

Production of cloned human leukocyte interferon by Bacillus subtilis: optimal production is connected with restrained growth.

Bacillus subtilis, transformed with a plasmid containing the human alpha-2 (leukocyte) interferon gene, was cultivated in batch and continuous culture in a complex medium. In continuous culture with dissolved oxygen of less than 10% of air saturation, the extracellular interferon titer decreased sharply when the growth rate was lower or higher than the optimal one (mu = 0.14 h-1). Thus, a relatively low growth rate was best for extracellular interferon production, and oxygen limitation enhanced interferon production. The mean output rate in batch culture after successful harvest was 20 X 10(6) IU/liter per h and the maximal output rate in continuous culture was 14 X 10(6) IU/liter per h.

Bacillus subtilis↗
PubMed1984

Structure of the cell surface of the yeast Candida tropicalis and its relation to hydrocarbon transport.

The surface structure of the hydrocarbon-utilizing yeast Candida tropicalis was investigated by scanning and transmission electron microscopy (SEM and TEM respectively). The sample preparation technique was based on a rapid cryofixation without any addition of cryoprotectants. In subsequently freeze-dried samples the surface structure was analysed by scanning electron microscopy. Thin sections were prepared from freeze substituted samples. Both techniques revealed hair-like structures at the surface of hydrocarbon-grown cells. The hairy surface structure of the cells was less expressed in glucose-grown cells and it was absent completely after proteolytic digestion of the cells. When cells were incubated with hexadecane prior to cryofixation a contrast-rich region occurred in the hair fringe of thin sections as revealed by TEM. Since these structures were characteristic for hexadecane-grown cells and could not be detected in glucose-grown or protease-treated cells it was concluded that they originate from hexadecane adhering to the cell surface and are functionally related to hexadecane transport. The structure of the surface and its relation to hydrocarbon transport are discussed in view of earlier results on the chemical composition of the surface layer of the cell wall.

Candida↗
PubMed1984

The cytochrome P450-containing monooxygenase of Trichosporon cutaneum: occurrence and properties.

Trichosporon cutaneum metabolizes glucose purely oxidatively and cytochrome P450 was not detected in the reduced CO-difference spectrum of whole cells. However, in the isolated microsomal fraction the corresponding monooxygenase was present as shown by the appearance of cytochrome P450, NADPH-cytochrome c(P450) reductase and cytochrome b5. The absorption maximum of the terminal oxidase in the reduced CO-difference spectrum shifted between 447 and 448 nm. Derepression of biosynthesis of all components was achieved by transition of the cells from carbon- to oxygen-limited growth in continuous culture. The monooxygenase exhibited aminopyrine demethylation activity but not omega-hydroxylation activity of lauric acid. With respect to the growth limiting nutrient (carbon and oxygen respectively), mitochondrial cytochrome content showed an analogous behavior as cytochrome P450 and cytochrome b5.

Candida↗
PubMed1984

Pseudomonas aeruginosa biosurfactant production in continuous culture with glucose as carbon source.

Rsan-ver, a strain of Pseudomonas aeruginosa isolated at this department, was used for the development of a continuous process for biosurfactant production. The active compounds were identified as rhamnolipids. A final medium for production was designed in continuous culture by means of medium shifts, since the formation of surface-active compounds was decisively influenced by the composition and concentration of the medium components. In the presence of yeast extract, biosurfactant production was poor. For the nitrogen-source nitrate, which was superior to ammonium, an optimum carbon-to-nitrogen ratio of ca. 18 existed. The iron concentration needed to be minimized to 27.5 micrograms of FeSO4 X 7H2O per g of glucose. A carbon-to-phosphate ratio below 16 yielded the maximum production of rhamnolipids. The final productivity dilution rate diagram indicated that biosurfactant production was correlated to low growth rates (dilution rate below 0.15 h-1). With a medium containing 18.2 g of glucose liter-1, a biosurfactant concentration (expressed as rhamnolipids) of up to 1.5 g liter-1 was obtained in the cell-free culture liquid.

Ammonium Sulfate↗
PubMed1984

Metabolic conditions determining the composition and catalytic activity of cytochrome P-450 monooxygenases in Candida tropicalis.

In the microsomal fraction of Candida tropicalis cells, two distinct monooxygenases were detected, depending on the growth conditions. The distinction of the two monooxygenases was evident from: (i) the absorption maxima in the reduced CO difference spectra of the terminal oxidases (cytochromes P-450 and P-448); (ii) the contents of the monooxygenase components (cytochromes P-450/P-448, NADPH-cytochrome c (P-450) reductase, and cytochrome b5) and (iii) the catalytic activity of the complete system (aliphatic hydroxylation and N-demethylation activity). The occurrence of the respective monooxygenases could be related to the carbon source (n-alkanes or glucose). Oxygen limitation led to a significant increase of cytochrome P-450/P-448 content, independent of the carbon source utilized by the cells. An improved method for the isolation of microsomes enabled us to demonstrate the presence of cytochrome P-448 in glucose-grown cells.

Alkanes↗
PubMed1983

Rapid Degradation of Isolated Lignins by Phanerochaete chrysosporium.

Phanerochaete chrysosporium degraded purified Kraft lignin, alkali-extracted and dioxane-extracted straw lignin, and lignosulfonates at a similar rate, producing small-molecular-weight ( approximately 1,000) soluble products which comprised 25 to 35% of the original lignins. At concentrations of 1 g of lignin liter, 90 to 100% of the acid-insoluble Kraft, alkali straw, and dioxane straw lignins were degraded by 1 g of fungal mycelium liter within an active ligninolytic period of 2 to 3 days. Cultures with biomass concentrations as low as 0.16 g liter could also completely degrade 1 g of lignin liter during an active period of 6 to 8 days. The absorbance at 280 nm of 2 g of lignosulfonate liter increased during the first 3 days of incubation and decreased to 35% of the original value during the next 7 days. The capacity of 1 g of cells to degrade alkali-extracted straw lignin under optimized conditions was estimated to be as high as 1.0 g day. This degradation occurred with a simultaneous glucose consumption rate of 1.0 g day. When glucose or cellular energy resources were depleted, lignin degradation ceased. The ability of P. chrysosporium to degrade the various lignins in a similar manner and at very low biomass concentrations indicates that the enzymes responsible for lignin degradation are nonspecific.

Journal Article↗
PubMed1979

Plasma membrane from Candida tropicalis grown on glucose or hexadecane. II. Biochemical properties and substrate-induced alterations.

Isolated plasma membranes from the yeast Candida tropicalis grown on two different carbon sources (glucose or hexadecane), had similar contents of protein (60% of total dry weight), lipid (21-24%) and carbohydrates (16-21%). Sodium dodecyl sulphate gel electrophoresis of the membrane proteins revealed 17 and 19 protein bands, respectively, for glucose and hexadecane grown cells. There were marked differences in RF values and relative peak heights between the two gels. Sterols and free fatty acids were the major components of the plasma membrane lipids. Phospholipid content was less than 2% of total plasma membrane lipids. Membrane microviscosity, as determined by fluorescence polarization, was very high (16.6 P). Fatty acid determination of membrane lipids by gas chromatography showed a significant increase of C16 fatty acids in plasma membranes of cells grown on hexadecane. Reduced-oxidized difference spectra demonstrated the presence of a b-type cytochrome in both Saccharomyces cerevisiae and C. tropicalis plasma membranes. Its concentration in C. tropicalis plasma membranes was three-fold greater in cells grown on hexadecane than in glucose grown cells.

Alkanes↗
PubMed1978

Plasma membranes from Candida tropicalis grown on glucose or hexadecane. I. Isolation, identification and purification.

Plasma membranes from Candida tropicalis grown on glucose or hexadecane were isolated using a method based on the difference in surface charge of mitochondria and plasma membranes. After mechanical disruption of the cells, a fraction consisting of mitochondrial and plasma membrane vesicles was obtained by differential centrifugation. Subsequently the mitochondria were separated from the plasma membrane vesicles by aggregation of the mitochondria at a pH corresponding to their isoelectric point. Additional purification of the isolated plasma membrane vesicles was achieved by osmolysis. Surface charge densities of mitochondria and plasma membranes were determined and showed substrate-dependent differences. The isolated plasma membranes were morphologically characterized by electron microscopy and, as a marker enzyme, the activity of Mg2+-dependent ATPase was determine. By checking for three mitochondrial marker enzymes the plasma membrane fractions were estimated to be 94% pure with regard to mitochondrial contamination.

Adenosine Triphosphatases↗
PubMed1978

Chemical and structural alterations at the cell surface of Candida tropicalis, induced by hydrocarbon substrate.

The surface-localized polysaccharide of alkane-grown cells of Candida tropicalis was identified as mannan containing approximately 4% covalently linked fatty acids. Glucose-grown cells lacked the mannan-fatty acid complex. The surface structure of alkane-grown cells showed a radial arrangement of the wall polymers, with protruding parts. The cell surface of glucose-grown cells was smooth, with a coherent outer limit. The mannan was localized by using concanavalin A. Masking of the mannan with concanavalin A reduced the binding affinity of the surface for alkane, indicating the involvement of the surface-localized mannan-fatty acid complex in the binding of alkanes.

Alkanes↗
PubMed1977

Component from the cell surface of the hydrocarbon-utilizing yeast Candida tropicalis with possible relation to hydrocarbon transport.

A polysaccharide-fatty acid complex was isolated from the cell surface of Candida tropicalis growing on alkanes. This complex was solubilized by Pronase treatment of whole cells. A decrease in alkane-binding affinity was observed after Pronase treatment, resulting in 10 to 12% of the yeast dry cell weight being released as polysaccharide. The isolated polysaccharide contained 2.5% fatty acids. C. tropicalis and Saccharomyces cerevisiae grown with glucose contained only traces of fatty acids in the corresponding polysaccharide fraction. The fatty acids were not removed from the polysaccharide moiety by gel filtration. Extraction of the polysaccharide with chloroform-methanol showed that fatty acids were covalently bound to the polysaccharide. The amphipathic nature of the isolated polysaccharide and the hydrocarbon-induced formation suggest a possible role in alkane metabolism.

Alkanes↗
PubMed1976

The mode of interaction between the substrate and cell surface of the hydrocarbon-utilizing yeast Candida tropicalis.

A method for the measurement of the affinity of the cell surface to hydrocarbons is described. The affinity was basically unaffected by different pH values and temperature as well as by the chain length of the substrate. The contact time required for saturation of the cell surface with substrate was 30 sec. Cells grown on glucose showed a 25% lower adsorption capacity compared to those grown on n-alkane. The glucose grown cells showed also a more distinguished dependence of the amount of adsorbed hydrocarbon on the quality of the emulsion. The interaction between the substrate and cell surface turned out to be an adsorption that did not involve an enzymatic reaction. These results led to the conclusion that a lipopolysaccharide moiety present at the cell surface is responsible for the affinity.

Adsorption↗