PubMed Health⌕ Search

Biomedical subjects

T Schewe

Publications and source records attributed to T Schewe.

At least 109 records · Page 6Linked to original sources
PubMed1980

[Electron transport particles from bovine heart as a test system in toxicological studies].

14 standard respiratory inhibitors and substances of toxicological interest were tested on the NADH oxidase and the succinate-cytochrome c oxidoreductase systems of beef heart electron transfer particles (ETP) in the presence and absence of human serum albumin (HSA). HSA did not influence the half-inhibition concentrations by cyanide, amytal and antimycin A. It had little effect on the inhibition by rotenone or carboxin, whereas the inhibition by free fatty acids and monoglyceride was greatly decreased. Lindan and DDT exerted a marked inhibition of the NADH oxidase system in the absence of HSA; the inhibition was weaker but still considerable in the presence of HSA. In the presence of HSA 10(-4) M DDT but not Lindan inhibited also the succinate-cytochrome c reductase system. The results show that ETP may be a useful test object in toxicological studies.

Amobarbital↗
PubMed1979

The lipoxygenase of reticulocytes. Purification, characterization and biological dynamics of the lipoxygenase; its identity with the respiratory inhibitors of the reticulocyte.

A lipoxygenase has been purified from rabbit reticulocyte-rich anaemic blood cells. It possesses a molecular weight of 78 000 and an isoelectric point of 5.5 and contains 5% neutral sugars and two iron atoms per enzyme molecule. The lipoxygenase has proved to be identical with the inhibitors of respiratory proteins described formerly. The actions of the lipoxygenase on linoleic acid, phospholipids, mitochondrial and erythrocyte membranes and electron transfer particles were studied. A special feature of the reticulocyte lipoxygenase is the suicidal character of its action on lipids. With electron transfer particles the reticulocyte lipoxygenase causes a loss of acid-labile sulfur which accompanies respiratory inhibition; the strong respiratory inhibition is not exerted by soybean lipoxygenase. The reticulocyte lipoxygenase acts preferably on mitochondrial membranes as compared with cell membranes of the erythrocyte; erythrocyte cytosol moderates the action on mitochondrial membranes. Furthermore, the lipoxygenase reaction can concomitantly and irreversibly inactivate sulfhydryl enzymes as demonstrated with muscle glyceraldehyde-3-phosphate dehydrogenase. The occurrence of the lipoxygenase here described is restricted to reticulocytes; very low amounts were observed in bone marrow and no lipoxygenase was detectable in normal blood. During the course of an experimental anaemia the lipoxygenase is produced owing to superinduction in large amounts, which may persist for a long time since they escape inactivation. Preliminary evidence was obtained for the occurrence of other lipoxygenases in tissues of lung, spleen, kidney and also epithelial tumours.

Amino Acids↗
PubMed1979

[Selectivity of action of the lipoxygenase from rabbit reticulocytes on mitochondria and erythrocyte membranes].

Whereas the lipoxygenase from rabbit reticulocytes caused a large formation of malonyl dialdehyde (MDA) with rat liver mitochondria, erythrocyte ghosts were attacked only slightly independently of their type of preparation. The formation of MDA was not enhanced by release of spectrin-actin from the ghosts. The lipoxygenase did not give rise to hemolysis of intact erythrocytes. The formation of MDA was increased by heat treatment of the ghosts. Addition of cholesterol to a phospholipid emulsion inhibited the formation of MDA by the reticulocyte lipoxygenase. These results indicate that both lipid-protein interactions and the cholesterol content of the membranes may be involved in the preferential attack of the lipoxygenase on mitochondrial membranes.

Animals↗
PubMed1979

[In vitro maturation of rabbit reticulocytes: oxygen consumption reaction].

With a simple experimental system the changes of endogenous, antimycin A-suppressed, oligomycin-suppressed and antimycin A-resistant oxygen consumption are studied during the maturation of intact cells of the 6th day of bleeding. All functional characteristics of oxygen consumption decrease during maturation. The rate of decrease is strongly increased by high inorganic phosphate concentrations (125 mM). This effect is most obvious for the oligomycin-suppressed and the endogenous respiration. The degree of uncoupling of non-incubated cells is 14%. During 24 h incubation it rises to 75%. Inorganic phosphate accelerates the increase of uncoupling during maturation. Reticulocytes of the 4th day of bleeding are characterized by a higher respiratory capacity and also by a higher rate of maturation of antimycin A-suppressed and endogenous respiration. The degree of uncoupling does not increase during maturation. This may be attributed to the low lipoxygenase activity of these cells. 25% of the endogenous oxygen consumption of unmatured cells are antimycin A-resistant. This type of respiration declines by 50% in 4 h incubation irrespective of inorganic phosphate concentrations and day of bleeding. In nitrogen all functional characteristics of respiration during the maturation decline more rapidly than in oxygen. The antimycin A-resistant respiration, however decreased more slowly and reached 50% after 12 h. A pH dependence of maturation (maximum at pH 8.4) was found for the endogenous and the antimycin A-suppressed respiration. The degree of uncoupling rises most quickly at pH 7.4. This is possibly related to the pH maximum of lipoxygenase.

Animals↗
PubMed1979

[Free fatty acids as inhibitors of the respiratory chain in testicular homogenates].

The supernatants of the 440 000 . g . min centrifugation of homogenates of rat, bull and boar testicles and sperm inhibit the NADH-oxidase activity of non-phosphorylating submitochondrial particles (ETP). Whereas no inhibitory activity was observed with young rats (150 g), a marked inhibition was detected with heavier animals. The inhibitory activity of testicles was located in the microsomal fraction. The reaction of the testicular inhibitor with the ETP is initiated by an instant reversible binding followed by a slow irreversible inhibition of the electron transport. The reason of the time-dependence is neither an interaction between the enzymes of the ETP and those of the microsomal electron transport nor a slow degradation of the ETP by microsomal phospholipases. Some observations indicate an indirect involvement of phospholipase via the formation of free fatty acids (FFA). The inhibitory fraction could be solubilized from the microsomes both by sodium cholate treatment and by ethanol extraction. After separation of the lipid classes by chromatography on silica gel and gas-chromatographic analysis the inhibitory fraction was identified as a mixture of free fatty acids (FFA) of different chain lengths and degree of saturation. Thus a new effect of FFA on the mitochondrial electron transport has been detected which is different from other actions known up till now. The degradation of the phospholipids of the endoplasmic reticulum in the spermatozoa may be the source of the enhanced formation of FFA. An inhibition of the cell respiration presumably does not occur in vivo. The high FFA level in the testicular homogenates of sexually mature animals is a consequence of an intensive FFA metabolism, especially of high phospholipase activity.

Animals↗
PubMed1979

[Energy metabolism of the rat renal cortex, as measured by incubation in various substrates].

Different substrate mixtures were investigated for their effect on energy metabolism using sections of the rat renal cortex. Simultaneous determination of adenine nucleotide concentrations and determination of the damage quotient of oxidative phosphorylation proved to be appropriate parameters for selecting substrate mixtures that have a favorable effect on energy metabolism. A mixture of albumin (1 mM) and octanoate (5.6 mM) with electrolytes proved to be adequate. The extent of oxygen consumption (60%) and 14CO2 formation (75%) argues in favor of the metabolization of this mixture; a damage quotient of 23% and general constancy of the concentration of high-energy compounds render prospective their testing in animal experiments. Addition of dicarbosylic acids increase the antimycin A resistant oxygen consumption without any energy conservation being demonstrable. Therefore, these substrates should not be used for conservation.

Adenine Nucleotides↗
PubMed1977

Degradation of mitochondria by cytosolic factors in reticulocytes.

The degradation process of mitochondria in rabbit reticulocytes proceeds predominately directly in the cytosol rather than in secondary lysosomes as judged by electronmicroscopy. At least five cytosolic protein factors are present in reticulocytes, which could be related to the degradation of mitochondria: the two inhibitory proteins of the respiratory chain RF and RC and three enzymes which cause a lysis of mitochondria in vitro (lipoxygenase, proteinase, phospholipase A). The properties of these factors are the subject of this paper. A hypothetic scheme of the degradation of mitochondria in reticulocytes is proposed. The degradation of mitochondria in reticulocytes is viewed as a complex interplay of various cytosolic factors and the functional state of the mitochondrial membranes. The lipoxygenase damages the membranes and triggers the penetration of the respiratory inhibitors. In this manner, a catastrophic cycle is initiated which leads to the complete breakdown of the mitochondria.

5-Aminolevulinate Synthetase↗
PubMed1977

[Electron transport particles from beef-heart mitochondria as a test system for inhibitors of the respiratory chain].

Respiratory inhibitors exert a potentially biocidic action on all aerobic organisms. Therefore the systematic search for them and the elucidation of their mechanism of action is of great importance. The non-phosphorylating electron transfer particles (ETP) according to Crane et al. are a suitable test object for this aim. A standardized preparation of ETP from beef heart is described and characterized enzymatically. The ETP show a variety of advantages in comparison with other systems; their field of application is broad. Owing to the absence of bypasses of the respiration, particles from animals are more suitable than those from plants for the search for fungicides and herbicides which inhibit the respiratory chain. With relatively little expense, the two standard assay systems proposed (NADH oxidase and succinate-cytochrome c oxidoreductase) pick up with certainty all inhibitors of the main pathway of the respiratory chain; they are useful for screening studies. The system proposed is also suitable for the analysis of the exact site and the mechanism of action of respiratory inhibitors. Furthermore, ETP can be used to obtain parameters of the hydrophobicity of drugs as well as for toxicological studies.

Animals↗
PubMed1977

Some properties of the lipoxygenase from rabbit reticulocytes.

A lipoxygenase was enriched from the stoma-free supernatant of rabbit reticulocytes. The enzyme causes drastic deterioration of mitochondrial membranes. The release of matrix enzymes is paralleled by formation of products of lipid peroxidation. The enzyme reacts with isolated phospholipds and free cis-unsaturated fatty acids. Some properties were determined: molecular weight, isoelectric point, temperature and pH-dependence and Km value for linoleic acid. The enzyme is inhibited by reaction products and a variety of inhibitors, especially antioxidants and chelating agents.

Animals↗
PubMed1977

[Action of respiratory inhibitors on the electron transport system of Escherichia coli].

Bacteria of two strains of Escherichia coli (Q13 and MRE 600) were disintegrated by aluminium oxide. The influence of the respiratory inhibitors RF (a protein from reticulocytes), carboxin, Dexon (fungicides), thenoylftrifluoroacetone (TTFA), rotenone, antimycin A, myristic acid and monolaurin was tested on the succinate oxidase and the NADH oxidase system, respectively, of the membrane preparation obtained in this way as well as on the NADH oxidase activity of the cytosol. Among the inhibitors listed, only TTFA (5mM) inhibited the succinate oxidase system and Dexon (10 miconr), monolaurin (100 micron) and myristic acid (100 micron) inhibited the NADH oxidase system of the membranes. KCN (10 micron) inhibited both NADH oxidase systems. The inhibitory effects by monolaurin and myristic acid were prevent by human serum albumin and were markedly weaker than those on beef heart mitochondrial particles under similar conditions. The results argue for a divergent structure of the iron-sulphur proteins in the dehydrogenase regions of the electron transport system in comparison with animal and plant mitochondria and, moreover, confirm the specificity of RF and carboxin as well as the nature of Dexon as a group reagent on pyridine nucleotide dependent flavin enzymes.

Antimycin A↗
PubMed1977

[Mechanism of action of the inhibition of pyridine-nucleotide-dependent flavine enzymes using the systemic fungicide Dexon].

The actions of Dexon on the NADH-ferricyanide oxidoreductase and the NADPH oxidase system of electron transfer particles (ETP) from beef heart as well as on the NADPH-cytochrome c oxidoreductase from brewer's yeast (Saccharomyces carlsbergensis Hansen) were investigated. The inhibition of the NADH dehydrogenase activity of ETP and that of the yeast enzyme correspond with respect to the following characteristics: 1) increase in the inhibition, 2) enhancement of the Dexon sensitivity by one order of magnitude after preincubation in the presence of NAD(P)H, 3) irreversibility of the inhibition, 4) no detectable changes in the spectral properties and in coenzyme activity of FMN after acid extraction from Dexon-treated enzyme. The inhibition of the NADH dehydrogenase activity of ETP is diminished by both NAD+ and FMN. However, no interaction of Dexon with NAD(P)H or FMN could be detected in the absence of enzyme or apoenzyme. The concentration of half-inhibition by Dexon for the yeast enzyme corresponds with its FMN concentration. It is proposed that both apoenzyme, NAD(P)H and FMN are involved in the interaction with Dexon. Possible mechanisms of binding are both complanar complexations of the ring systems and a triazene formation between FMNH2 and Dexon. The NADPH oxidase activity of the ETP is partly inhibited; the share inhibited by Dexon may represent the pathway via the transhydrogenase reaction.

Animals↗
PubMed1977

Activity of the respiratory inhibitor RF in human red cells in anaemia.

Stroma-free haemolysates of red cells from patients with acute or latent anaemia inhibit the NADH oxidase activity of submitochondrial particles from beef heart. The inhibitory activities appeared significantly more frequently in anaemic patients than in normal persons and are likely due to the action of a factor which is identical or similar to the inhibitory protein RF present in rabbit reticulocytes. The possible use of the inhibitor assay for clinical purpose is under discussion.

Acute Disease↗
PubMed1977

[Purification and characterization of the respiratory inhibitor RF from rabbit reticulocytes].

In the stroma-free hemolysate of rabbit reticulocytes there exists a respiratory inhibitor (RF) of protein nature. It could be purified by the following procedure: (NH4)2SO4-precipitation leads to DEAE-Sephadex A-50-chromatography leads to isoelectric focusing leads to gelfiltration on Sephadex G-200. In addition to the activity the identity of the inhibitor could be proved immunologically at all steps of the purification. A molecular weight of about 80,000 was determined by gelelectrophoresis in the SDS-mercaptoethanol-system. The protein has an IP of 5.55--5.65 and consists of one polypeptide chain. This could be shown both by SDS-gelelectrophoresis and by estimation of only one N-terminal amino acid residue (glycine). Only after oxidation with performic acid the amino acid analysis of the protein gives reproducible values. The sum of weight-% is about 80 (without Tyr). The polarity of the protein with 41 mol-% agrees with the polarity of soluble globular proteins investigated by other authors. Acid hydrolysis without preceeding performic acid oxidation gives a sum of amino acid residues of only 35--45 weight-%, the glycoprotein nature of the inhibitor could be shown by staining the SDS-gels with Schiff's reagents and by carbohydrate determination with anthrone reagent.

Animals↗