Search PubMed⌕ Search

Biomedical subjects

F Scheller

Publications and source records attributed to F Scheller.

At least 37 records · Page 2Linked to original sources
PubMed1986

Enzymatic determination of isocitrate by amperometric monitoring of the rate of oxygen consumption.

A coupled enzymatic method elaborated for NAD+-dependent dehydrogenases has been adapted for NADP+-dependent isocitrate dehydrogenase, in combination with amperometric measurements. The isocitrate dehydrogenase activity dependent linearly on the isocitrate concentration in the range 0-2 X 10(-4) M. Application of this method affords a sensitive estimation of isocitrate even in turbid liquids such as fermentation broths.

Electrodes↗
PubMed1985

Enzyme electrode for urea with amperometric indication: Part I--Basic principle.

A novel method for amperometric determination of substrates of hydrolytic enzymes has been developed. As an example the pH dependence of electrochemical oxidation of hydrazine in the Tafel region was combined with the urease catalysed splitting of urea to construct an amperometric membrane electrode for urea. The characteristic features of this sensor are: a linear dependence of the current of hydrazine oxidation on hydrogen ion concentration (as opposed to the logarithmic response of potentiometric sensors), linear urea concentration-signal relationship between 0.8 and 35 mmol/litre sample concentration, a response time of about 20 s, a relative standard deviation of 1% and measuring frequency up to 40 samples/h with an electrode operational stability of 2 weeks. Calibration curves for aqueous urea solutions are given as functions of starting pH, urease and hydrazine concentration and the potential dependence of the signal was determined.

Buffers↗
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↗
PubMed1983

[Uric acid determination in dilute serum with an enzyme electrochemical and enzyme-free sensor].

The paper describes the development of electrochemical methods for analytical determination of uric acid basing on amperometric sensors: with an uricase enzyme electrode, termed "electrochemical-enzymatic" method; with an enzyme-free electrode by indication of the anodic oxidation of uric acid, termed "electrochemical" method. The comparison of analytical quality of both methods shows a sufficient specificity, precision, and accuracy. They show a good correlation with regard to the specific uricase-catalase reference method (UCM): yelectr./enz. = (0.943 xUCM + 19.8) mu mol/l; r = 0.9948 yelectr. = (0.964 xUCM + 6.31) mu mol/l; r = 0.9917 The analysis by the "electrochemical" method can be done with a higher frequency of samples per hour completely without need of enzyme. Both methods are principally suitable for an application in analytic biochemical laboratories.

Electrochemistry↗
PubMed1982

[Effect of infusions on blood glucose determinations--comparative determinations by the DAB7(D.L.) methods and a newly developed glucometer].

The influence of 22 various infusions on the determination of the blood glucose by means of glucometer and DAB 7 (D.L.)-methods [o-toluidine, hexocyanoferrat (III)] was investigated. Only the principle of the newly developed apparatus glucometer is not disturbed by infusions and represents an alternative solution for surgery, urology, paediatrics and intensive medicine, particularly since the measuring value is present at any time in few seconds.

Blood Glucose↗
PubMed1981

[Determination of glucoamylase activity using an enzyme electrode].

Both, the differing definitions of glucoamylase activity and the different determination of the fragment, glucose, preclude a comparison of literature data. Specific enzymatic determination of the fragment, glucose, with an enzyme electrode is proposed. The contribution describes the manufacture of an enzyme electrode from a commercial pO2-electrode and immobilized GOD. The measurement may be carried out by kinetic determination of utilized oxygen or oxygen peroxide formed. The continuous measurement proposed for serial experiments is made via a calibration curve, whose regression coefficient was determined to be 0.999. Depending on the enzyme activity, the reaction time is between 15 s and 3 min.

Electrodes↗
PubMed1980

Glucose oxidase bienzyme electrodes for ATP, NAD+, starch and disaccharides.

Based on a glucose oxidase sensor for determination of glucose several glucoseoxidase bioenzyme electrodes have been developed. Enzymes producing glucose by hydrolysis of saccharides (glucamylase, invertase, cellulase) as well as glucose consuming systems (hexo-kinase, glucose dehydrogenase) have been coupled to glucose oxidase. The function of the bienzyme systems was demonstrated by concentration measurements (blood glucose, maltose, ATP, NAD+, starch) and enzyme activity measurements (alpha-amylase, ATPase, lactate dehydrogenase).

Adenosine Triphosphate↗
PubMed1980

[Glucose determination in diluted whole blood using an enzyme electrode].

The construction and operation of a measuring device containing an enzyme electrode is described. Glucose oxidase is enclosed in an acrylamide film by means of photopolymerization. The maximal increase of the anodic current of the H2O2 being formed in the enzyme reaction serves as measuring signal. The device gives for diluted serum and blood correlation coefficients above 0,99 according to the methods given in the German Pharmacopeia 7. The measuring time for each specimen is roughly 90 s, the serial variation coefficient 2%.

Blood Glucose↗
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↗