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H Degn

Publications and source records attributed to H Degn.

12 recordsLinked to original sources
PubMed1991

Effects of alcohols on the respiration and fermentation of aerated suspensions of baker's yeast.

The immediate effects of externally added alcohols on CO2 production and O2 consumption of suspensions of washed, aerated baker's yeast were studied by stopped-flow membrane inlet mass spectrometry. Glucose-supported fermentation was progressively inhibited by increasing ethanol concentration (0-20%, v/v). The inhibition by ethanol was quite different from that observed for acetaldehyde; thus it is unlikely that toxicity of the latter can account for the observed effects. For five different alkanols (methanol, ethanol, 1-propanol, 2-propanol and 1-butanol) increasing inhibition of anaerobic fermentation was correlated with increased partition coefficients into a hydrophobic milieu. This suggests that the action of ethanol is primarily located at a hydrophobic site, possibly at a membrane. Results for respiratory activities were not as definite as for those for anaerobic metabolism because some alkanols act as respiratory substrates as well as giving inhibitory effects.

Aerobiosis↗
PubMed1991

The parasitic flagellates Trichomonas vaginalis and Tritrichomonas foetus produce indole and dimethyl disulphide: direct characterization by membrane inlet tandem mass spectrometry.

The use of a membrane inlet triple quadrupole mass spectrometer revealed indole as an end product in the growth medium of cultures of the cattle parasite Tritrichomonas foetus and the human parasite Trichomonas vaginalis: formation of indole is enhanced in the presence of added tryptophan. Two different clinical isolates of Trich. vaginalis also produce dimethyl disulphide. Electron impact ionization yielded complex fragmentation mixtures, but the facility for analysis of daughter ions enabled unequivocal assignments. Chemical ionization gave [M + 1]+ species, and tandem mass spectrometry produced identification through daughter ions. The method provides a rapid single-step procedure for the characterization of microbial products without the need for preliminary separation and derivatization.

Animals↗
PubMed1979

The effect of inhibitors on the oxygen kinetics of terminal oxidases of Acanthamoeba castellanii.

1. Respiration of growing cultures of Acanthamoeba castellanii is inhibited less than 60% by azide (35 mM); the respiration of early-exponential-phase cultures differs from that of late-exponential-phase cultures in being stimulated by up to 120% by low concentrations (less than 1 mM) of this inhibitor. Azide (0.5 mM) plus 1 mM-salicylhydroxamic acid gives 80% inhibition of respiration in early- or late-exponential-phase cultures. 2. Lineweaver-Burk plots of 1/v against 1/[O2] for growing and stationary-phase cultures give values of less than 1 muM for the apparent Km for oxygen. 3. These values are not significantly altered when determined in the presence of 1 mM-salicylhydroxamic acid. 4. Higher values (greater than 7 muM) for apparent Km values for oxygen were obtained in the presence of azide, which gives non-linear Lineweaver-Burk plots. 5. Competitive inhibition of respiration by CO occurs with Ki 2.4 muM. 6. The results are discussed in terms of the presence of three terminal oxidases in this organism, namely two oxidases with high affinities for oxygen (cytochrome c oxidase of the main phosphorylating electron-transport chain and the salicylhydroxamic acid-sensitive oxidase) and a third oxidase with a low affinity for oxygen, sensitive to inhibition by cyanide but not by azide or salicylhydroxamic acid. The relative contributions to oxygen utilization by these oxidases change during the growth of a batch culture.

Amoeba↗
PubMed1978

Steady-state kinetics of laccasse from Rhus vernicifera.

The steady-state kinetics of laccasse (monophenol, dihydroxyphenylalanine: oxygen oxidoreductase, EC 1.14.18.1) from the lacquer tree Rhus vernicifera is investigated using the respirograph method to produce Lineweaver-Burk plots of oxygen consumption rate against oxygen concentration. A ping-pong mechanisms is established. The kinetic constants obtained according to the model is in close agreement with the corresponding values obtained from earlier studies on the transient reactions between the reduced enzyme and oxygen (Andréasson, L.E., Brändén, R. and Reinhammar, B. (1976) Biochim. Biophys. Acta 438, 370--379) and between the oxidized enzyme and reducing substrates (Andréasson, L.E. and Reinhammar, B. (1976) Biochim. Biophys. Acta 445, 579--597).

Catechol Oxidase↗
PubMed1978

Oscillatory kinetics of the peroxidase-oxidase reaction in an open system. Experimental and theoretical studies.

1. The oscillations in the peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7)-catalyzed reaction between NADH and O2 are undamped when the reaction is carried out in a system open to both substrates and when 2,4-dichlorophenol and methylene blue are present in the solution. 2. The waveform of the oscillations changes when the concentration of peroxidase is varied. 3. The waveforms obtained experimentally can be simulated by a branched chain reaction model in which the branching is quadratic. 4. A correlation between the present knowledge of the reaction and the model can be made by combining well established and hypothetical reaction steps into a few reaction schemes. A selection among schemes however, is not possible at the present time. 5. Compound III participates in the reaction as an active intermediate. This is possible because dichlorophenol stimulates the break down of compound III.

Computers↗
PubMed1977

Steady-state oxygen kinetics of terminal oxidases in Trypanosoma mega.

Steady-state oxygen kinetics of Trypanosoma mega reveal the presence of 3 oxidases. These include an oxidase which is sensitive to salicylhydroxamic acid (SHAM) but insensitive to sodium azide. This oxidase could be the L-alpha glycerophosphate oxidase present in bloodstream trypanosomes. In addition, and oxidase is present wthich is azide-sensitive but SHAM-insensitive. This oxidase is inhibited by CO and is probably cytochrome aa3. A 3rd oxidase is insensitive to both azide and SHAM but is inhibited by CO and is possibly cytochrome o. Reciprocal plots of T. mega reveal the presence of 2 oxidases that are inhibited by CO. These results are discussed in the light of previous evidence suggesting the presence of several oxidases and a branched electron transport system in T. mega.

Animals↗
PubMed1976

The effect of oxygen concentration on the steady-state kinetics of the solubilized cytochrome c oxidase.

1. The steady-state kinetics of ascorbate oxidation as a function of oxygen concentration was measured with a solubilized cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) preparation. 2. Linear double reciprocal plots were obtained at various fixed concentrations of ascrobate, cytochrome c and cytochrome aa3. 3. The results are interpreted in terms of an oxidase model similar to that put forward by Minnaert in 1961 (Minnaert, K. (1961) Biochim. Biophys. Acta 50, 23-34). 4. The Km for oxygen at infinite cytochrome c concentration is 0.95 muM and the intramolecular rate constant for the transfer of electrons from cytochrome c to cytochome aa3 is 400 s(-1). According to the model, this implies that the second order rate constant for the reaction between oxygen and the oxidase is 9.5 X 10(7)M(-1)-s(-1).

Animals↗
PubMedDate not supplied

Oscillatory CO2 evolution in glycolysing yeast extracts.

The rate of formation of carbon dioxide in cytoplasmic yeast extracts in an open system with continuous infusion of glucose was measured by membrane inlet mass spectrometry during glycolytic oscillations. The rate of CO2 production rose in the first third of each cycle to a maximum of about 100 mumol per ml yeast extract per hour and subsequently diminished to a final level of about 50 mumol per h. Measurements of the NADH light absorption under the same conditions revealed oscillations of relaxation type. The phase of high CO2 production could be related to the phase of the high NADH level, giving evidence that the flux in glycolysis is increased during the phase of high NADH concentration. Only half of the amount of injected glucose was metabolized to CO2 during the sustained oscillation, although free glucose did not accumulate.

Carbon Dioxide↗