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Biomedical subjects

F Scheller

Publications and source records attributed to F Scheller.

48 records · Page 3Linked to original sources
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↗
PubMed1975

Studies on electron transfer between mercury electrode and hemoprotein.

The electrochemical behaviour of ferricytochrome c, metmyoglobin and methemoglobin was studied using d.c., a.c. and differential pulse polarography, and controlled potential electrolysis. 1. The three hemoproteins yield d.c. polarographic steps, and peaks in differential pulse polarograms, the height of which is proportional to concentration. The charge transfer is influenced by strong adsorption. 2. The concentration dependence of the a.c. polarograms indicates structural changes in the adsorbed molecules. 3. The reduction products of controlled potential electrolysis of metmyoglobin and methemoglobin have absorption spectra identical with the native control samples. The affinity for oxygen and the cooperativity in hemoglobin are not affected by the reaction at the electrode. 4. The charge transfer proceeds via adsorbed, already reduced, molecules to freely diffusible proteins.

Binding Sites↗
PubMed1975

[Polarographic studies on the peroxidase activity of liganded deuterohemin].

The peroxidase activity of deuterohemin and deuterohemin complexes relative to the substrates pyrogallol and ascorbic acid was studied using d.c. polarography in aqueous solution. Imidazole and pyridine served as complex ligands. In the absence of the ligands, a continual rise in the substrate conversion rate with increasing H2O2 initial concentration is observed. Imidazole or pyridine were found to considerably increase the peroxidase activity of deuterohemin at low H2O2 concentrations. At high H2O2 concentrations, the dependence of the reaction rate on H2O2 concentration shows a bend, the reaction rate being in each case higher than that of free hemin under the same conditions. The reason of this fact is discussed to be a retarded formation of activated H2O2 hemin-ligand complexes at high H2O2 concentrations.

Deuteroporphyrins↗
PubMedDate not supplied

Cardiovascular and endocrine alterations after masturbation-induced orgasm in women.

OBJECTIVE: The present study investigated the cardiovascular, genital, and endocrine changes in women after masturbation-induced orgasm because the neuroendocrine response to sexual arousal in humans is equivocal. METHODS: Healthy women (N = 10) completed an experimental session, in which a documentary film was observed for 20 minutes, followed by a pornographic film for 20 minutes, and another documentary for an additional 20 minutes. Subjects also participated in a control session, in which participants watched a documentary film for 60 minutes. After subjects had watched the pornographic film for 10 minutes in the experimental session, they were asked to masturbate until orgasm. Cardiovascular (heart rate and blood pressure) and genital (vaginal pulse amplitude) parameters were monitored continuously throughout testing. Furthermore, blood was drawn continuously for analysis of plasma concentrations of adrenaline, noradrenaline, cortisol, prolactin, luteinizing hormone (LH), beta-endorphin, follicle-stimulating hormone (FSH), testosterone, progesterone, and estradiol. RESULTS: Orgasm induced elevations in cardiovascular parameters and levels of plasma adrenaline and noradrenaline. Plasma prolactin substantially increased after orgasm, remained elevated over the remainder of the session, and was still raised 60 minutes after sexual arousal. In addition, sexual arousal also produced small increases in plasma LH and testosterone concentrations. In contrast, plasma concentrations of cortisol, FSH, beta-endorphin, progesterone, and estradiol were unaffected by orgasm. CONCLUSIONS: Sexual arousal and orgasm produce a distinct pattern of neuroendocrine alterations in women, primarily inducing a long-lasting elevation in plasma prolactin concentrations. These results concur with those observed in men, suggesting that prolactin is an endocrine marker of sexual arousal and orgasm.

Adult↗
PubMedDate not supplied

[Use of cytochrome P-450 and ferroporphyrin as catalyzers in hydroxylation reactions jointly with electrochemical systems].

The mechanism of P-450 catalyzed reactions is discussed. They are shown not to be true peroxidase reactions. Liver microsome P-450 is capable of oxidizing such substrates as benzphenamine, amidopyrine and p-nitroanisole via molecular oxygen reduced on the cathode. The methods of stabilizing the enzymic system by means of immobilization of microsomes or isolated components are described. The possibility of coupling the enzymic and the electrochemical system is considered. The approaches to the modelling of the cytochrome P-450 catalytic activity with the aid of ferroporphyrine are proposed.

Catalysis↗