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Biomedical subjects

R Renneberg

Publications and source records attributed to R Renneberg.

30 records · Page 2Linked to original sources
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↗
PubMed1983

Study of H2O2-supported N-demethylations catalyzed by cytochrome P-450 and horseradish peroxidase.

H2O2-supported oxidative demethylation reactions catalyzed by cytochrome P-450 and horseradish peroxidase have been compared. In contrast to peroxidase catalyzed reactions no free substrate radicals could be detected by EPR stopped flow measurements in demethylation reactions catalyzed by highly purified cytochrome P-450 although the rate of product formation for both enzyme systems was identical. These findings cause doubts in a general peroxide dependent demethylation mechanism valid for all hemoproteins and in the hypothesis that free substrate radicals are principally formed during cytochrome P-450 catalysis.

Aminopyrine↗
PubMed1979

Comparison of the peroxidatic activity of cytochrome P-450 with other hemoproteins and model compounds.

The H2O2 dependent catalysis of cytochrome P-450 was compared with the catalytic mechanism of horse radish peroxidase, methemoglobin and iron protoporphyrin complexes. A relatively stable intermediate being comparable to compound I of horse radish peroxidase is formed in the case of iron porphyrin complexes, methemoglobin and probably cytochrome P-450. In the case of peroxidase compound II is the more stable intermediate. This could be the reason for the different catalytic properties of peroxidase on the one hand and iron porphyrin complexes, methemoglobin and cytochrome P-450 on the other hand.

Animals↗
PubMed1979

Electrochemical investigations on the oxygen activation by cytochrome P-450.

The application of cytochrome P-450 in substrate conversion is complicated both due to the limited stability and the cofactor regeneration problems. To overcome the disadvantages of NADPH consumption the transfer of the reduction equivalents from an electrode into the cytochrome P-450-system was studied: 1. NADPH was cathodically reduced at a mercury pool electrode. By immobilization of NADP on dialdehyde Sephadex the reductive recycling was possible. 2. Different forms of reduced oxygen were produced by the cathode: a) The reaction of O2- with deoxycorticosterone yields a carboxylic acid derivative. In contrast the cytochrome P-450 catalyzed NADPH-dependent reaction with the same substrate gives corticosterone, O2- represents only an intermediate in the activation of oxygen and is not the "activated oxygen" species. b) Molecular oxygen was reduced to HO2- and H2O2, respectively. The interaction of adsorbed cytochrome P-450 on the electrode surface with the reduced oxygen species in the absence of NADPH was studied. The electrochemically generated peroxide seems to be more active than added H2O2. 3. In a model of electro-enzyme-reactor several substrates were hydroxylated by microsomal cytochrome P-450 with cathodically reduced oxygen which substitutes NADPH.

Animals↗
PubMed1978

Aspects of application of cytochrome P-450 and related systems in substrate hydroxylation.

Extrapolating the recent progress in the near future the extensive utilization of cofactor-dependent enzymes (enzymes of the 3rd generation) for solving economic or medical problems will be restricted by the difficulties of cofactor regeneration. Real possibilities exist in analytical systems, for instance enzyme electrodes. In the present paper a special case of overcoming the cofactor regeneration in P-450 catalyzed substrate hydroxylation is demonstrated: The peroxide-dependent reaction gives the same products as obtained under physiological conditions; that is why in an electro-enzyme-reactor producing hydrogen peroxide by cathodic oxygen reduction a considerable simplification of the multi-enzyme complex is possible by omitting electron transfer proteins. At present the main problem is the instability of the terminal oxidase. Attempts are being made to solve these problems by immobilizing the protein or substituting P-450 by other hemoproteins or iron porphyrin derivatives.

Animals↗
PubMedDate not supplied

The peroxidatic function of liver microsomal cytochrome P-450: comparison of hydrogen peroxide and NADPH-catalysed N-demethylation reactions.

Fifteen different secondary and tertiary methyl amines have been examined as substrates for the cytochromes P-450 of rat-liver microsomes to determine the similarities or differences between the NADPH and oxygen-dependent N-demethylation reaction and the reaction occurring in the presence of hydrogen peroxide. No apparent correlation of the rates of formaldehyde formation using the two different conditions of oxidation was observed. The types of cytochromes P-450 were altered by using rat-liver microsomes from animals treated with various inducing agents. No obvious predictable dependence on the animals treated with various inducing agents. No obvious predictable dependence on the type of cytochrome P-450 present was obtained for the hydrogen peroxide-supported peroxidatic reaction. It is concluded that the hydrogen peroxide-dependent N-demethylation reaction occurs by a reaction mechanism distinct from that occurring during the mixed-function oxidase activity of cytochrome P-450 obtained in the presence of NADPH and oxygen.

Animals↗