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Biomedical subjects

A Boveris

Publications and source records attributed to A Boveris.

At least 145 records · Page 8Linked to original sources
PubMed1976

Localization of peroxidase activity in Trypanosoma cruzi microbodies.

Electron microscopic observation of Trypanosoma cruzi epimastigotes reveals the presence of microbody-like structures (microperoxisomes) in which 3,3'-diaminobenzidine (DAB) is peroxidized to electron-opaque material. The role of peroxidase in DAB peroxidation is supported by the enzyme demonstration in disrupted epimastigotes and the microbody-containing cell fractions.

Animals↗
PubMed1976

Role of ubiquinone in the mitochondrial generation of hydrogen peroxide.

Antimycin-inhibited bovine heart submitochondrial particles generate O2- and H2O2 with succinate as electron donor. H2O2 generation involves the action of the mitochondrial superoxide dismutase, in accordance with the McCord & Fridovich [(1969) j. biol. Chem. 244, 6049-6055] reaction mechanism. Removal of ubiquinone by acetone treatment decreases the ability of mitochondrial preparations to generate O2- and H2O2, whereas supplementation of the depleted membranes with ubiquinone enhances the peroxide-generating activity in the reconstituted membranes. Addition of superoxide dismutase to ubiquinone-reconstituted membranes is essential in order to obtain maximal rates of H2O2 generation since the acetone treatment of the membranes apparently inactivates (or removes) the mitochondrial superoxide dismutase. Parallel measurements of H2O2 production, succinate dehydrogenase and succinate-cytochrome c reductase activities show that peroxide generation by ubiquinone-supplemented membranes is a monotonous function of the reducible ubiquinone content, whereas the other two measured activities reach saturation at relatively low concentrations of reducible quinone. Alkaline treatment of submitochondrial particles causes a significant decrease in succinate dehydrogenase activity and succinate-dependent H2O2 production, which contrasts with the increase of peroxide production by the same particles with NADH as electron donor. Solubilized succinate dehydrogenase generates H2O2 at a much lower rate than the parent submitochondrial particles. It is postulated that ubisemiquinone (and ubiquinol) are chiefly responsible for the succinate-dependent peroxide production by the mitochondrial inner membrane.

Acetone↗
PubMed1976

Mitochondrial production of hydrogen peroxide in Saccharomyces cerevisiae.

Intact mitochondria isolated from bakers' yeast and showing respiratory control by ADP, released H2O2 to the suspending medium at rates of 1.2.2.2 nmol/min per mg of protein depending on the mitochondrial metabolic condition. Release of H2O2 from mitochondria increased 1.3 times in swollen mitochondria and 1.2 times after osmotic shock, i.e., when the outer membrane was damaged. Under physiological conditions, yeast cytochrome c peroxidase, mainly located in the intermembrane space, utilized about 53-55% of the H2O2 generated by the respiratory chain at the inner membrane, partially preventing H2O2 diffusion to the cytosol. Apparently, the outer mitochondrial membrane was highly permeable to H2O2. It is claimed that the risk of cell injury due to H2O2, O-2 and HO is slightly higher in the stationary phase than in the logarithmic phase of growth.

Antimycin A↗
PubMed1973

The mitochondrial generation of hydrogen peroxide. General properties and effect of hyperbaric oxygen.

1. Pigeon heart mitochondria produce H(2)O(2) at a maximal rate of about 20nmol/min per mg of protein. 2. Succinate-glutamate and malate-glutamate are substrates which are able to support maximal H(2)O(2) production rates. With malate-glutamate, H(2)O(2) formation is sensitive to rotenone. Endogenous substrate, octanoate, stearoyl-CoA and palmitoyl-carnitine are by far less efficient substrates. 3. Antimycin A exerts a very pronounced effect in enhancing H(2)O(2) production in pigeon heart mitochondria; 0.26nmol of antimycin A/mg of protein and the addition of an uncoupler are required for maximal H(2)O(2) formation. 4. In the presence of endogenous substrate and of antimycin A, ATP decreases and uncoupler restores the rates of H(2)O(2) formation. 5. Reincorporation of ubiquinone-10 and ubiquinone-3 to ubiquinone-depleted pigeon heart mitochondria gives a system in which H(2)O(2) production is linearly related to the incorporated ubiquinone. 6. The generation of H(2)O(2) by pigeon heart mitochondria in the presence of succinate-glutamate and in metabolic state 4 has an optimum pH value of 7.5. In states 1 and 3u, and in the presence of antimycin A and uncoupler, the optimum pH value is shifted towards more alkaline values. 7. With increase of the partial pressure of O(2) to the hyperbaric region the formation of H(2)O(2) is markedly increased in pigeon heart mitochondria and in rat liver mitochondria. With rat liver mitochondria and succinate as substrate in state 4, an increase in the pO(2) up to 1.97MPa (19.5atm) increases H(2)O(2) formation 10-15-fold. Similar pO(2) profiles were observed when rat liver mitochondria were supplemented either with antimycin A or with antimycin A and uncoupler. No saturation of the system with O(2) was observed up to 1.97MPa (19.5atm). By increasing the pO(2) to 1.97MPa (19.5atm), H(2)O(2) formation in pigeon heart mitochondria with succinate as substrate increased fourfold in metabolic state 4, with antimycin A added the increase was threefold and with antimycin A and uncoupler it was 2.5-fold. In the last two saturation of the system with oxygen was observed, with an apparent K(m) of about 71kPa (0.7-0.8atm) and a V(max.) of 12 and 20nmol of H(2)O(2)/min per mg of protein. 8. It is postulated that in addition to the well-known flavin reaction, formation of H(2)O(2) may be due to interaction with an energy-dependent component of the respiratory chain at the cytochrome b level.

Animals↗
PubMed1972

The cellular production of hydrogen peroxide.

1. The enzyme-substrate complex of yeast cytochrome c peroxidase is used as a sensitive, specific and accurate spectrophotometric H(2)O(2) indicator. 2. The cytochrome c peroxidase assay is suitable for use with subcellular fractions from tissue homogenates as well as with pure enzyme systems to measure H(2)O(2) generation. 3. Mitochondrial substrates entering the respiratory chain on the substrate side of the antimycin A-sensitive site support the mitochondrial generation of H(2)O(2). Succinate, the most effective substrate, yields H(2)O(2) at a rate of 0.5nmol/min per mg of protein in state 4. H(2)O(2) generation is decreased in the state 4-->state 3 transition. 4. In the combined mitochondrial-peroxisomal fraction of rat liver the changes in the mitochondrial generation of H(2)O(2) modulated by substrate, ADP and antimycin A are followed by parallel changes in the saturation of the intraperoxisomal catalase intermediate. 5. Peroxisomes supplemented with uric acid generate extraperoxisomal H(2)O(2) at a rate (8.6-16.4nmol/min per mg of protein) that corresponds to 42-61% of the rate of uric acid oxidation. Addition of azide increases these H(2)O(2) rates by a factor of 1.4-1.7. 6. The concentration of cytosolic uric acid is shown to vary during the isolation of the cellular fractions. 7. Microsomal fractions produce H(2)O(2) (up to 1.7nmol/min per mg of protein) at a ratio of 0.71-0.86mol of H(2)O(2)/mol of NADP(+) during the oxidation of NADPH. H(2)O(2) is also generated (6-25%) during the microsomal oxidation of NADH (0.06-0.025mol of H(2)O(2)/mol of NAD(+)). 8. Estimation of the rates of production of H(2)O(2) under physiological conditions can be made on the basis of the rates with the isolated fractions. The tentative value of 90nmol of H(2)O(2)/min per g of liver at 22 degrees C serves as a crude approximation to evaluate the biochemical impact of H(2)O(2) on cellular metabolism.

Adenosine Diphosphate↗