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Biomedical subjects

T Schewe

Publications and source records attributed to T Schewe.

At least 127 records · Page 7Linked to original sources
PubMed1976

[Action of several respiration inhibitors on the tetramethyl-p-phenyldiamine short-circuit pathway in nonphosphorylating electron transport particles in the bovine heart].

Non-phosphorylating electron transfer particles from beef heart according to CRANE et al. possess the ability to oxidize succinate via the artificial TMPD bypass of the respiratory chain. The respiratory inhibitors TTFA, carboxin, tridemorph and the inhibitory protein RF from rabbit reticulocytes act both on the normal succinate oxidase and on the bypass. The presence of antimycin A diminishes the inhibition of carboxin on the bypass, likely by way of the increase of the degree of reduction in the iron-sulphur proteins. The inhibition by an isatin-beta-isothiosemicarbazone acting on the complex III of the succinate oxidase system is relieved by TMPD analogous to antimycin A.

Animals↗
PubMed1976

[The systemic fungicide tridermorph as an inhibitor of the respiratory chain of electron transfer particles from beef heart mitochondria].

Tridemorph (N-tridecyl-2,6-dimethylmorpholine) inhibits both the NADH-oxidase and the succinate-cytochrome c oxydoreductase system of non-phosphorylating electron transfer particles from beef heart. The concentration required for half-inhibition amounted to 3,4 muM and 24 muM respectively. Two different sites of action in the respiratory chain could be localized by means of difference spectroscopy and measurements of enzymic activities in various partial systems. The inhibition of the NADH-ubiquinone oxydoreductase activity as well as the suppression of the NADH-induced reduction of all cytochromes on the one hand and the insensitivity of the NADH-ferricyanide oxydoreductase system on the other argue in favour of a site of action similar to rotenone. The partial suppression of the succinate-induced reduction of cytochrome b with simultaneous complete inhibition of the reduction of the other cytochromes indicate an additional site of action analogous to antimycin A. Both inhibitory actions appeared instantaneously after the addition of tridemorph and were counteracted by serum albumin. Furthermore, tridemorph inhibited the oxydation of external ferrocytochrome c but not that of ascorbate/tetra-methyl-p-phenylene-diamine-HCI (TMPID) showing that it is not a true inhibitor of the cytochrome oxidase. The TMPD-induced bypass of the succinate oxidation was inhibited as well. The possible role of the inhibition of the main pathway of the respiratory chain for the fungicidal action of tridemorph is discussed.

Animals↗
PubMed1975

[Distribution of endogenous inhibitors of the respiratory chain in plants].

70 phosphate buffer extracts of various plant tissues of 40 species as well as of 2 bacteria were tested for the presence of endogenous inhibitors of the respiratory chain. Electron transfer particles (ETP) from beef heart mitochondria served as test object. The NADH oxidase (spectrophotometrically) and the succinate oxidase activity (manometrically) were measured. Inhibitory activities could be detected in all the plant species tested, but there were quantitative differences by orders of magnitude. The inhibitory effects were more frequent and higher in the NADH oxidase system than those in the succinate oxidase system. The highest inhibitory activities were observed with blossoms of Forsynthia intermedia, male blossoms of Corylus avellana, inflorescences of Brassica oleracea, fronds of Pteridium aquilinum and gallnuts of Quercus. The specific inhibitory activities (related to the dry mass of the extracts) suggest very efficient inhibitors having concentrations of half-inhibition in the muM-range. With 6 extracts the inhibitory activity on the NADH oxidase system was completely destroyed by boiling (Brassica oleracea, Amoracia rusticana, leaves of Digitalis purpurea, roots of Allium cepa, fruit pips of Malus domestica and mushrooms of Lactarius vellereus). The results with some plant species (Bryophyllum daigremonteanum, Allium cepa, male blossoms of Corylus avellana, Pteridium aquilinum) suggest a biological dynamics of the inhibitory activity. The inhibitor from Bryophyllum was partially characterized with regard to its mode of action. The following supposed biological functions of endogenous respiratory inhibitors of plants are discussed: 1. Involvement in the degradation of mitochondria in the course of differentiation, maturation and involution processes as well as in biologically controlled senescence processes; 2. A switch-over to the alternative mitochondrial respiratory pathway; 3. Induction and maintenance of a resting metabolism, e.g. in dormancy, by action as growth inhibitors; 4. Action as phytoncides (phytoallexines) for the defense against parasites.

NADH, NADPH Oxidoreductases↗
PubMed1975

[Action of the systemic fungicide dexon on several NADH dehydrogenases].

The fungicide dexon (p-dimethylaminobenzenediazosulfonate, Na-salt) inhibits the NADH oxidase activity of submitochondrial particles (ETP) from beef heart (semi-inhibition concentration 1.4 muM), while the succinate oxidase activity is unaffected. Measurements of the activity of several enzymatic partial reactions of the respiratory chain of ETP suggest that dexon acts directly on the flavine of NADH dehydrogenase. Soluble NADH-cytochrome c-oxidoreductase (MAHLER) and rotenone-insensitive NADH ubiquinone reductase are also inhibited by dexon. At low concentrations of dexon, inhibition of ETP starts slowly only after addition of NADH. Preincubation without NADH increases the amount of inhibition, but does not prevent the time delay. It is assumed that an electron flux through the respiratory chain, or reduction of flavine is prerequisite for the reaction of dexon with the action site. Furthermore, dexon inhibits the NADH dehydrogenase located at the outer surface of the inner membrane of plant mitochondria, accessible to extramitochondrial NADH and insensitive to rotenone, as has been shown on isolated mitochondria from cauliflower (Brassica oleracea L). In addition, dexon inhibits selectively the NADH dehydrogenase of the DT diaphorase (ERNSTER) from rat liver cytosol. In contrast, the dicoumarol-insensitive NADH dehydrogenase (ZINSMEYER et al.) from rat liver cytosol, the NADH-cytochrome b5-reductase (STRITTMATTER) from rat liver microsomes, the rotenone-insensitive NADH-cytochrome c-oxidoreductase of the outer membrane of rat liver mitochondria, soluble NADH-oxidase from Escherichia coli, and NADH-dehydrogenase from human erythrocytes are not inhibited. The results suggest that dexon is a group reagent to certain pyridine nucleotide-dependent flavine enzymes.

Animals↗
PubMed1975

[Presence of a lysis factor of mitochondria in rabbit reticulocytes].

Incubation of isolated rat liver and beef heart mitochondria together with a fraction of nonhaemoglobin proteins from rabbit reticulocytes (reti-AS) leads to drastic structural damages such as a deformation and disruption of the outer membranes as well as a disappearance of the cristae structure. The vacuolized forms obtained in this manner reveal striking similarities to the known degradation ones of reticulocyte mitochondria in situ and after isolation of them. The extent of the lysis of mitochondria depends on the amount of reti-AS and on the temperature. The lysis is caused by a protein factor (MLF) which is not identical with the respiratory inhibitor RF present in the reti-AS as well. Like RF, MLF disappears during the maturation process of reticulocytes to erythrocytes. MLF triggers the penetration of RF into the mitochondria and thus the inhibition of the succinate oxidase and the NADH oxidase activity. EDTA inactivates RF but not MLF. MLF is bound to electron transfer particles from beef heart mitochondria. The experimental conditions used are supposed to be a model for the degradation of mitochondria in situ during the maturation process of reticulocytes.

Animals↗
PubMed1975

On the mechanism of the cyanide-insensitive alternative pathway of respiration in fungi and higher plants and the nature of the alternative terminal oxidase.

In connection with investigations on the mechanism of action of the systemic fungicide carboxin a new hypothesis was developed on the mechanism of the cyanide-insensitive pathway of respiration, which is widely distributed in fungi und higher plants, and on the nature of the alterative terminal oxidase. Based on own experimental results which are in concordance with the properties of the alternative pathway described in the literature, it is assumed that the nonheme-iron-sulfurprotein (FeSPp) of the succinodehydrogenase, which is located on the main route of the cytochrome mediated respiration, is the alternative terminal oxidase itself. This property seems to be based on the ability for autoxidation in some organisms where the Fe-atoms are oxygenized and reach the maximal coordination number of 6. By this mechanism it is explainable that carboxin which also attacks the normal electron flow at the FeSPp of the succinodehydrogenase is able to inhibit simultaneously under certain circumstances the cyanide-insensitive respiration organisms sensitive to carboxin.

Anilides↗