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Biomedical subjects

O Volfová

Publications and source records attributed to O Volfová.

At least 19 recordsLinked to original sources
PubMed1997

Characterization of phytase produced by Aspergillus niger.

The extracellular activity of Aspergillus niger phytase at the end of the growth phase was 132 nkat/mL in a laboratory bioreactor. The purified enzyme has molar mass approximately 100 kDa, pH optimum at 5.0, temperature optimum at 55 degrees C and high pH and temperature stability. The Km for dodecasodium phytate, calcium phytate and 4-nitrophenyl phosphate are 0.44, 0.45 and 1.38 mmol/L, respectively. The enzyme is noncompetively inhibited by inorganic monophosphate (Ki = 2.85 mmol/L) and by Cu2+, Zn2+, Hg2+, Sn2+, Cd2+ ions and strongly by F- ones; it is activated by Ca2+, Mg2+ and Mn2+ ions. The substrate specificity of phytase is broad with the highest affinity to calcium phytate.

6-Phytase↗
PubMed1994

Phytase from Aspergillus niger.

132 microorganisms, isolates from soil and decayed fruits, were tested for phytase production. All isolates intensively producing active extracellular phytase were of fungal origin. The most active fungal isolates with phytase activity were identified as Aspergillus niger. At the end of the growth phase, the extracellular phytase activity produced by A. niger strain 92 was 132 nkat/mL, with strain 89 it was 53 nkat/mL. In both strains the extracellular enzyme activity exhibited two marked activity optima at pH 1.8 and 5.0 and a temperature optimum at 55 degrees C.

6-Phytase↗
PubMed1992

Effect of increasing methanol concentrations on physiology and cytology of Candida boidinii.

Concentration of methanol in the medium strongly affected not only the physiology but also the cytology of Candida boidinii strain 2 cells in a methanol-limited chemostat at a constant dilution rate D 0.1/h and at low pH 3.0. The formation of large cubic peroxisomes with high alcohol oxidase (AO) activity observed at low methanol concentration (S0 3 g/L) disappeared on increasing the methanol concentration in the inflow medium. The AO activity in the cells sharply decreased, followed by accumulation of riboflavin phosphate and residual methanol in the medium. The activity of catalase was relatively stable. At methanol concentration S0 > KI (KI equal to 12 g methanol per L), which included a substantial increase in methanol dissimilation, documented by higher formaldehyde and formate dehydrogenase activities and by lower yield coefficient on methanol, the yeast cells contained large lobe-shaped peroxisomes and a smaller number of larger mitochondria. The cells formed pseudomycelium with a thick septum between the mother and daughter cells.

Candida↗
PubMed1991

Characterization of catalase-negative mutants of methylotrophic yeast Hansenula polymorpha.

Three recently isolated catalase-negative mutants of Hansenula polymorpha lost the ability to grow on methanol but grew in media containing glucose, ethanol or glycerol. Their incubation in a medium with methanol resulted in an accumulation of hydrogen peroxide and cell death. During growth of a catalase-negative mutant in chemostat on a mixture of methanol and glucose, neither H2O2 accumulation nor cell death were observed up to the molar ratio of 10:1 of the two substrates. Cytochrome-c peroxidase and NADH-peroxidase activities were detected in the cells. In methylotrophic yeasts, catalase seems to be an enzyme characteristic of the metabolism of methanol but not needed for the metabolism of multicarbon substrates. The hydrogen peroxide produced during growth of the mutants on mixed substrates is detoxified by cytochrome-c peroxidase and other peroxidases.

Catalase↗
PubMed1989

Alcohol oxidase of methylotrophic thermo- and acidotolerant yeast Hansenula sp.

Electrophoretic analysis of alcohol oxidase purified from the methylotrophic thermo- and acidotolerant yeast Hansenula sp. revealed the presence of two active forms of the enzyme with molar mass 440 kg/mol (major component) and 724 kg/mol (minor component). A subunit M of the enzyme was found to be 72 kg/mol. Two active forms of the enzyme found by electrophoresis seem to be caused by dissociation of the octameric form to the tetramer under alkaline conditions. Studies of alcohol oxidase showed a kinetic variability of the enzyme with respect to its Km. It is proposed that the variability of Km is caused by enzyme binding to formaldehyde.

Alcohol Oxidoreductases↗
PubMed1982

Influence of pH on the formation and location of beta-glucosidase in Aspergillus terreus grown on ceLlulose.

Wild strain of Aspergillus terreus is very good producer of beta-glucosidase. It produces 15 nkat/mL (0.9 IU/mL) of extraceLlular beta-glucosidase at pH 5.0. The medium pH level strongly affects the production and binding of beta-glucosidase on the cells and on residual cellulose. At pH 4.0 the rate of enzyme synthesis and the level of total activity is highest but 60-75% of this activity is bound. At higher pH levels the enzyme is mainly released to the medium.

Aspergillus↗
PubMed1982

Anaerobic degradation of cellulose and formation of methane.

The existing knowledge of anaerobic digestion of cellulose-containing wastes and methane formation is reviewed. Mutual relationships between the individual phases of this complex process and the mechanism of methane biosynthesis are discussed in three sections: (1) Non-methanogenic phase and digestion of cellulose; (2) methanogenic phase and methanogenesis; (3) mixed cultures and their advantages.

Anaerobiosis↗
PubMed1981

Cell growth and cellulase production in Trichoderma viride on microcrystalline cellulose.

The production of CM and FP cellulases was studied during the growth of a wild strain of Trichoderma viride on microcrystalline cellulose. Part of the enzymes was found to be released into the medium while another part remained bound to the cell. Bound cellulases are released into the medium at the stage of cell lysis which takes place in the post-stationary phase. In this period extracellular CM and FP cellulases attain maximum activities. When the hyphae are subjected to a cold shock, maximum cellulase activity is detected already at the beginning of the stationary phase. an indirect method of dry cell mass determination showed that during exponential growth of cells on microcrystalline cellulose the mumax was 0.23 and the yield coefficient was 41%.

Cellulase↗
PubMed1981

Kinetics of cellulase production in Trichoderma viride on microcrystalline cellulose.

During the cultivation of a wild strain of T. viride on microcrystalline cellulose the synthesis of cell-bound FP cellulases precedes cell growth. During the growth they are released into the medium as extracellular enzymes. The rete of synthesis of extracellular FP cellulases increases during cell growth, reaching a maximum at the beginning of transition to the stationary phase when the cell growth rate decreases. In contrast to extracellular enzymes, the rate of synthesis of bound cellulases during active growth is almost constant. In the stationary phase the rate of synthesis of both FP cellulases drops sharply, creasing well before cell lysis sets in and before the maximum level of extracellular cellulases is attained.

Cellulase↗
PubMed1979

Selection of a yeast strain with optimal utilization of straw hydrolyzates.

The dry nonseparated straw hydrolyzates prepared by mild acid hydrolysis of milled straw contains 25--30% of reducing substances, mostly saccharides with prevalence of xylose. A strain utilizing the neutralized nonseparated hydrolyzates without any growth substances added was obtained by selection and long-term adaptation of an array of yeast strains. The strain, identified as Candida tropicalis 2838, exhibited high cell-growth rate and considerable yield of protein-rich biomass.

Animal Feed↗
PubMed1979

Growth of Candida tropicalis 2838 cells on straw hydrolyzates.

Improved strain of Candida tropicalis 2838 grows on nonseparated straw hydrolyzates with no addition of vitamins and trace elements at a specific growth rate mu = 0.34 and 44% yield coefficient (referred to reducing substances). The reducing substances in hydrolyzates contain predominantly monosaccharides (xylose, glucose, arabinose, mannose). Cells grown in this way are rich in proteins (62%) and essential amino acids (lysine, phenylalanine, leucine, threonine and valine). The product obtained under industrial conditions by fermentation of the nonseparated hydrolyzates contains 8--9% of proteins and it is a suitable supplement of fodder mixtures for monogastric domestic animals. Nutrition tests on rats and pigs indicated that this product can substitute the hay-flour, and, partially, blood-flour barley, and that the strain used is nonpathogenic.

Animal Feed↗
PubMed1975

Studies on methanol - oxidizing yeast. III. Enzyme.

Oxidation of methanol, formaldehyde and formic acid was studied in cells and cell-free extract of the yeast Candida boidinii No. 11Bh. Methanol oxidase, an enzyme oxidizing methanol to formaldehyde, was formed inducibly after the addition of methanol to yeast cells. The oxidation of methanol by cell-free extract was dependent on the presence of oxygen and independent of any addition of nicotine-amide nucleotides. Temperature optimum for the oxidation of methanol to formaldehyde was 35 degrees C, pH optimum was 8.5. The Km for methanol was 0.8mM. The cell-free extract exhibited a broad substrate specificity towards primary alcohols (C1--C6). The activity of methanol oxidase was not inhibited by 1mM KCN, EDTA or monoiodoacetic acid. The strongest inhibitory action was exerted by p-chloromercuribenzoate. Both the cells and the cell-free extract contained catalase which participated in the oxidation of methanol to formaldehyde; the enzyme was constitutively formed by the yeast. The pH optimum for the degradation of H2O2 was in the same range as the optimum for methanol oxidation, viz. at 8.5. Catalase was more resistant to high pH than methanol oxidase. The cell-free extract contained also GSH-dependent NAD-formaldehyde dehydrogenase with Km = 0.29mM and NAD-formate dehydrogenase with Km = 55mM.

Aerobiosis↗