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P Liebs

Publications and source records attributed to P Liebs.

7 recordsLinked to original sources
PubMed1990

Amperometric determination of ammonium ions with a microbial sensor.

A sensor for NH+4 ions has been developed, which consists of immobilized micro-organisms (Bacillus subtilis, Pseudomonas aeruginosa, Trichosporon cutaneum) in combination with an electrochemical transducer. This sensor is based on the measurement of acceleration of respiration after addition of NH+4 in the presence of glucose. The physiological background of this signal and its connection with NH+4 ion uptake and/or metabolism is discussed. The response time of the sensor is about 5-10 s for NH+4 ions. A linearity was observed between 0.005 and 0.15 mmol dm-3 NH+4 ions. The sensitivity of the sensor remained almost constant for 12 days. The sensor was used to determine NH+4 ions in a microbial fermentation broth.

Bacillus subtilis↗
PubMed1989

A novel L-glutamate oxidase from Streptomyces endus. Purification and properties.

A new flavoenzyme using molecular oxygen to oxidize L-glutamic acid has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the culture medium of Streptomyces endus. Hydrogen peroxide, 2-oxoglutaric acid and ammonia are formed as products. Among 25 amino acids tested including D-glutamic acid, L-glutamine and L-aspartic acid, only L-glutamic acid is converted. The molecular mass of the enzyme was estimated to be about 90 kDa by gel chromatography and 50 kDa by SDS/PAGE. The subunit contains 1 molecule noncovalently bound FAD. The absorption spectrum shows maxima at 273, 355 and 457 nm and the isoelectric point is at pH 6.2. The Km value for L-glutamic acid in air-saturated phosphate pH 7.0 was estimated to be 1.1 mM, the Km for oxygen was calculated to be 1.86 mM at saturating concentration of L-glutamic acid. The enzymic reaction is inhibited by Ag+ and Hg2+ ions. The enzyme described here distinctly differs from two microbial L-glutamate oxidases purified hitherto, with regard to extremely high substrate specificity and to the subunit structure.

Amino Acid Oxidoreductases↗
PubMed1988

Formation of some extracellular enzymes during the exponential growth of Bacillus subtilis.

The formation of the exoenzymes, neutral and alkaline proteinase as well as alpha-amylase of Bacillus subtilis, is characterized by the same time course. The exoenzyme formation starts in the exponential phase of growth by an excess of C and N sources. We assume that carbon metabolism of pyruvate is responsible for the exoenzyme formation during this growth phase. The proteinase formation at the transient and/or stationary phase of growth is related to amino acid limitation.

Alanine↗
PubMed1988

[Nitrogen regulation in microorganisms].

The central role of NH4+-assimilation in the microbial metabolization of several inorganic nitrogen sources and the regulation of its key enzymes--glutamate dehydrogenases (GDH--EC 1.4.1.2. and EC 1.4.1.4.), glutamine synthetase (GS--EC 6.3.1.2.) and glutamate synthase (GOGAT--EC 1.4.1.3.)--are presented. In excess of ammonia gramnegative bacteria as well as yeasts assimilate this ion in a NADH + H+ or NADPH + H+ dependent reaction by GDH. Under NH4+-limitation--in natural environments rather the rule than the exception--the ammonia assimilation is ATP dependent and catalyzed via GS and GOGAT. Subsequently the connection between the nitrogen metabolization and the resulting changes in the extracellular pH of growing yeast cultures is discussed. The stoichiometric exchange between NH4+ and H+ led to the assumption that in the physiological pH-range an energy dependent NH4+/H+ transport is the preferred++ mechanism of ammonia uptake for NH4+ excess as well as for NH4+ shortage.

Ammonia↗
PubMed1987

Formation of extracellular neutral proteinase and the stringent response in Bacillus subtilis.

The kinetics of extracellular neutral proteinase synthesis by an isogenic stringent (IS58) and a relaxed (IS56) strain of B. subtilis were compared. The specific enzyme formation rate by the stringent strain was higher than that of the relaxed one. Norvaline addition (1 mg/mL) induced the formation of pppGpp and ppGpp, respectively, as well as the appearance of extracellular neutral proteinase activities in cultures of the stringent strain IS58 and a strain with high proteinase production (ZF-178) only. These correlations support the suggestion that (p)ppGpp are involved in the regulation processes responsible for production of extracellular neutral proteinases by B. subtilis.

Bacillus subtilis↗
PubMed1985

An electrochemical method for determination of cell respiration.

The respiration of microorganisms was determined with a sensor composed of microorganisms and an oxygen electrode. The microorganisms (suspensions of about 100 microliters) are sedimented by centrifugation in a special tube on a very thin paper layer (diameter 4 mm). This paper layer is sandwiched between a polyethylene membrane and a dialysis membrane. A linear relationship is obtained between the current and the cell mass of Bacillus subtilis (between 0.05-0.35 mg dry weight per electrode preparation). When an assimilable substrate is added to the measuring solution the respiration rate is increased. It is possible to determine very fast changes in the respiration rates (1-5 sec). The application of this electrode system for investigations of the physiological state of cells during the growth cyclus is demonstrated.

Bacillus subtilis↗