Hans Degn

Chaos in biological systems

Chaos in Physiology: Health or Disease?.- Patterns of Activity in a Reduced Ionic Model of a Cell from the Rabbit Sinoatrial Node.- Oscillatory Plant Transpiration: Problem of a Mathematically Correct Model.- Bifurcations in a Model of the Platelet Regulatory System.- Chaos in a System of Interacting Nephrons.- Polypeptide Hormones and Receptors: Participants in and Products of a Two-parameter, Dissipative, Measure Preserving, Smooth Dynamical System in Hydrophobic Mass Energy.- Interplay Between Two Periodic Enzyme Reactions as a Source for Complex Oscillatory Behaviour.- Dynamics of Controlled Metabolic Network and Cellular Behaviour.- Periodic Forcing of a Biochemical System with Multiple Modes of Oscillatory Behaviour.- Periodic Behaviour and Chaos in the Mechanism of Intercellular Communication Governing Aggregation of Dictyostelium Amoebae.- Turbulent Morphogenesis of a Prototype Reaction-Diffusion System.- Periodic Solutions and Global Bifurcations for Nerve Impulse Equations.- Homoclinic and Periodic Solutions of Nerve Impulse Equations.- High Sensitivity Chaotic Behaviour in Sinusoidally Driven Hodgkin-Huxley Equations.- Forced Oscillations and Routes to Chaos in the Hodgkin-Huxley Axons and Squid Giant Axons.- Quantification of Chaos from Periodically Forced Squid Axons.- Chaos, Phase Locking and Bifurcation in Normal Squid Axons.- Chaos in Molluscan Neuron.- Pancreatic B-Cell Electrical Activity: Chaotic and Irregular Bursting Pattern.- Multiple Oscillatory States and Chaos in the Endogenous Activity of Excitable Cells: Pancreatic B-Cell as an Example.- Bifurcations in the Rose-Hindmarch and the Chay Model.- Dendritic Branching Patterns.- Chaos and Neural Networks.- Data Requirements for Reliable Estimation of Correlation Dimensions.- Chaotic Dynamics in Biological Information Processing: A Heuristic Outline.- Chaos in Ecology and Epidemiology.- Low Dimensional Storage Attractors in Epidemics of Childhood Diseases in Copenhagen, Denmark.- Periodicity and Chaos in Biological Systems: New Tools for the Study of Attractors.- Populations Under Periodically and Randomly Varying Growth Conditions.- Bi-fractal Basin Boundaries in Invertible Systems.- Homoclinic Bifurcations in Ordinary Differential Equations.- Characterization of Order and Disorder in Spatial Patterns.- Fractals, Intermittency and Morphogenesis.- Temperature Stability of Davydov Solitons.

Inhibition by ammonia of methane utilization in Methylococcus capsulatus (Bath)

SummaryThe kinetics of methane uptake by Methylococcus capsulatus (Bath) and its inhibition by ammonia were studied by stopped-flow membrane-inlet mass spectrometry. Measurements were done on suspensions of cells grown in high- and low-copper media. With both types of cells the kinetics of methane uptake are hyperbolic when oxygen is in excess. The apparent Km and Kmax for methane uptake are both higher in low-copper cells than in high-copper cells. Ammonia is a simple competitive inhibitor of methane uptake in high-copper cells when the oxygen concentration is above a few μM. The findings agree with the assumption that ammonia is a week alternative substrate for particulate methane monooxygenase. In low-copper cells the effect of ammonia is complicated and cannot be explained in terms of current assumptions on the mechanism of soluble methane monooxygenase. Our data indicate that ammonia inhibition is likely to be a more serious problem in connection with cultivation in low-copper medium than in high-copper medium.

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.

Digital Regulation of Gas Flow Rates and Composition of Gas Mixtures

A digital principle is described which permits a linear regulation of gas flow rate. The regulator unit consists of a set of on-off valves connected to parallel flow resistors. The conductivities of the resistors are 1, 2, 4, 8,...,n and combinations of the resisters give the flow rates 1, 2, 3, 4,..., 2 n -1. thus a stepwise regulation with a unit step of less then 1 percent of the maximal flow rate can be obtained by a step of 7 values and resisters. By using two ways valus and complementing with a second gas, binary mixtures of controlled composition (molor fraction) are produced. An apparatus is described which utilizes the above principle for mixing oxygen and nitrogen. The flow resisters are made of plastic tubing, and magentic values are used to permit electric control. The limitations of the applicability of tubler resistors due to nonlinear phenomena are discussed.

Steady-state kinetics of laccase from Rhus vernicifera

Abstract The steady-state kinetics of laccase (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 mechanism 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 (Andreasson, L.-E.; Branden, R.; and Reinhammar, B. (1976) Biochim. Biophys. Acta 438, 370–379) and between the oxidized enzyme and reducing substrates (Andreason, L.-E.; and Reinhammar, B. (1976) Biochim. Biophys. Acta 445, 579–597).

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 bakers 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.

Membrane inlet ion mobility spectrometry for on-line measurement of ethanol in beer and in yeast fermentation

Abstract A membrane inlet ion mobility spectrometric method was developed for on-line measurement of ethanol concentration in beer and in yeast fermentation. Main parts of the measurement system are an ion mobility spectrometer, M90, and a custom built membrane inlet. The M90 ion mobility spectrometer is unique in the sense that positive and negative ions are simultaneously measured at 6 different detection channels, 3 for positive ions and 3 for negative ions. The custom built membrane inlet utilized a microporous polypropylene membrane for sample introduction into the M90 instrument. The developed measurement system allowed analysis of ethanol at 0.05% ( v v ) levels, clearly sufficient for the applications reported here. Good signal linearity was observed at positive ion channels 1 and 3 in ethanol concentration range 0.2−10% ( v v ), calculated correlation coefficients were 0.989 and 0.999, respectively. Agreement between the ethanol concentration measured by membrane inlet ion mobility spectrometry and the values declared on the beer bottle labels was good. Reproducibility of signals of the detection channels which gave the best response for ethanol was excellent in ethanol concentration measurement of beer samples, coefficient of variation was 1% for all these channels. Membrane inlet ion mobility spectrometry was also shown to be capable of on-line ethanol measurement, confirmed by membrane inlet mass spectrometry, during yeast fermentations.

Membrane inlet mass spectrometry in pure and applied microbiology

Abstract Membrane inlet mass spectrometry is a well established, inexpensive technique for continuous measurement in solution of most gases of interest in microbial physiology and fermentor control. Significant progress has recently been made in extending the capability of the technique to the measurement of volatile organic compounds in aqueous solution. This paper is a review of the technique of membrane inlet mass spectrometry for the measurement of dissolved gases and volatile organic compounds and its use in laboratory research on microbial physiology and in fermentor monitoring.

Oxidative Detoxification of Hydrogen Sulphide Detected by Mass Spectrometry in the Soil Amoeba Acanthamoeba castellanii

Respiration of the soil amoeba Acanthamoeba castellanii is stimulated by low concentrations of H2S (< 17 Pa in the gas phase); consumption of H2S accompanies respiratory stimulation. Inhibition of the main respiratory chain by 1 mm-NaN3 prevents H2S consumption. At higher concentrations, H2S inhibits respiration incompletely; the inhibition is enhanced by 1 mm-salicylhydroxamic acid. Thus this organism has two means of protection against the potentially toxic gas: the ability to oxidize H2S, and the presence of alternative pathways of electron transport which are not blocked by this respiratory inhibitor.

Growth rate and methane affinity of a turbidostatic and oxystatic continuous culture ofMethylococcuscapsulatus (Bath)

SummaryA turbidostatic and oxystatic fermentation system was used to study the growth kinetic ofMethylococcuscapsulatus (Bath). Dissolved oxygen and methane concentrations were measured continuously with membrane inlet mass spectrometry. The specific growth rate was found to increase from 0.25 h−1 to 0.37 h−1 and the saturation constant for methane was found to decrease from 71 μM to 1.3 μM as the copper content of the medium was varied from a very low to a high value.