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Biomedical subjects

R Renneberg

Publications and source records attributed to R Renneberg.

7 recordsLinked to original sources
PubMed1991

Enzyme sensor-FIA-system for on-line monitoring of glucose, lactate and glutamine in animal cell cultures.

Enzyme sensors for glucose, lactate and glutamine were connected via flow-injection analysis (FIA) devices to two different bioprocesses. They were used for on-line process control of perfused bioreactor systems containing mammalian cell lines producing a monoclonal antibody and recombinant interleukin-2. The biosensor system gives direct access to important process data which can be used as control parameters for long term cell cultivation systems.

Animals↗
PubMed1991

Second generation biosensors.

Enzyme-membrane electrodes using glucose oxidase in combination with peroxide detection dominate in the field of laboratory analyzers for diluted samples. Using the same indication principle, extremely fast responding glucose sensors have been fabricated by covering thin metal electrodes with a porous enzyme layer. In the second generation auxiliary enzymes and/or co-reactants are coimmobilized with the analyte converting enzyme in order to improve the analytical quality and to simplify the performance. Following this line oxidizable interferences are suppressed by using a glucose oxidase/peroxidase complex which communicates with the electrode at a low working potential. Furthermore, fluctuations of pH or buffer capacity are ineffective when using a glucose oxidase/peroxidase layer covered fluoride FET in the potentiometric glucose determination. Enzymatic recycling of the analyte and/or accumulation of intermediates increase the sensitivity by several orders of magnitude. Inclusion of NAD bound to PEG in the glucose dehydrogenase layer allows a reagentless glucose measurement.

Biosensing Techniques↗
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↗