Biomedical subjects

A N Nosikov

Publications and source records attributed to A N Nosikov.

6 recordsLinked to original sources

PubMed2005

Isolation, purification, and characterization of nitrate reductase from a salt-tolerant Rhodotorula glutinis yeast strain grown in the presence of tungsten.

The salt-tolerant Rhodotorula glutinis yeast strain grew in medium containing nitrate, 1 mM tungsten, and trace amounts of molybdenum (as impurities from the reagents used). Isolation of electrophoretically homogenous preparation of nitrate reductase from the Rh. glutinis cells grown under these growth conditions is described. The isolated nitrate reductase is a molybdenum-containing homodimer with molecular mass of 130 kD, containing 0.177 mol of Mo per mol of the enzyme. The activity of the enzyme is maximal at pH 7.0 and 35-45 degrees C and is inhibited by low concentrations of azide and cyanide. The enzyme is almost insensitive to 1 mM tungsten.

Azides↗

PubMed2002

Tungsten-containing enzymes.

The biological importance of tungsten has been fully proved in the last decade due to isolation of a number of tungsten-containing enzymes (W-enzymes) from hyperthermophilic archaea. Tungsten was previously considered only as an antagonist of molybdenum, because the replacement of molybdenum by tungsten (due to their chemical similarity) leads to inactivation of molybdenum-containing enzymes (Mo-enzymes). In addition to the "true W-enzymes" in which tungsten cannot be replaced by molybdenum, recently some enzymes have been isolated which can use either molybdenum or tungsten in the catalytic process. This review briefly summarizes data on the participation of tungsten in catalysis by some enzymes and the structure of the active sites of W-enzymes.

Bacteria↗

PubMed2000

Nitrate reductase and nitrous oxide production by Fusarium oxysporum 11dn1 under aerobic and anaerobic conditions.

The fungus Fusarium oxysporum 11dn1 was found to be able to grow and produce nitrous oxide on nitrate-containing medium in anaerobic conditions. The rate of nitrous oxide formation was three to six orders of magnitude lower than the rates of molecular nitrogen production by common denitrifying bacteria. Acetylene and ammonia did not affect the release of nitrous oxide release. It was shown that under anaerobic conditions fast increase of nitrate reductase activity occurred, caused by the synthesis of enzyme de novo and protein dephosphorylation. Reverse transfer of the mycelium to aerobic conditions led to a decline in nitrate reductase activity and stopped nitrous oxide production. The presence of two nitrate reductases was shown, which differed in molecular mass, location, temperature optima, and activity in nitrate- and ammonium-containing media. Two enzymes represent assimilatory and dissimilatory nitrate reductases, which are active in aerobic and anaerobic conditions, respectively.

Aerobiosis↗

PubMed2000

Stimulation of nitrate reductase activity of the salt-tolerant yeast Rhodotorula glutinis by tungsten in the presence of molybdenum.

Tungsten in the presence of molybdenum stimulates nitrate reductase activity and growth of the salt-tolerant yeast Rhodotorula glutinis on medium with nitrates. Tungsten is not incorporated in proteins possessing nitrate reductase activity. A significant increase in molybdenum cofactor in cells grown on medium with equimolar amounts of molybdenum and tungsten may relate to the stimulatory action of tungsten.

Enzyme Stability↗

PubMedDate not supplied

[Kinetic method of tungsten analysis in tungsten-containing enzymes].

A highly sensitive method for tungsten detection in proteins based on the ability of this metal to catalyze the oxidation of with hydrogen peroxide is described. The method allows determining tungsten in protein samples in the concentration range of -0.05 to -0.4 microgram/ml. Molybdenum, at a concentration lower than half the concentration of tungsten, as well as iron, selenium, and pterin at concentrations -2.5 times higher than that of tungsten, had no effect on tungsten determination by this method.

Hydrogen Peroxide↗

PubMedDate not supplied

[Properties of nitrate reductase from Fusarium oxysporum 11dn1 fungi grown under aerobic and anaerobic conditions].

Production of nitrate reductase was studied in 15 species of microscopic fungi grown on a nitrate-containing medium. Experiments were performed with Fusarium oxysporum 11dn1, a fungus capable of producing nitrous oxide as the end product of denitrification. Moreover, a shift from aerobic to anaerobic conditions of growth was accompanied by a sharp increase in the activity of nitrate reductase. Studies of nitrate reductase from the mycelium of Fusarium oxysporum 11dn1, grown under aerobic and anaerobic conditions, showed that this enzyme belongs to molybdenum-containing nitrate reductases. The enzymes under study differed in the molecular weight, temperature optimum, and other properties. Nitrate reductase from the mycelium grown under aerobic conditions was shown to belong to the class of assimilatory enzymes. However, nitrate reductase from the mycelium grown anaerobically had a dissimilatory function. An increase in the activity of dissimilatory nitrate reductase, observed under anaerobic conditions, was associated with de novo synthesis of the enzyme.

Aerobiosis↗