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Biomedical subjects

L Mela

Publications and source records attributed to L Mela.

At least 37 records · Page 2Linked to original sources
PubMed1977

3-Nitropropionate, the toxic substance of Indigofera, is a suicide inactivator of succinate dehydrogenase.

We have shown that 3-nitropropionate, an isoelectronic analogue of succinate, is a suicide inactivator of succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1] as follows. (i) When rat liver mitochondria oxidize succinate in the presence of 3-nitropropionate carbanion, the rate of O(2) consumption decreases exponentially to a zero value. This pattern is duplicated by subsequent additions of mitochondria. The dependence of the apparent first-order rate constant for enzyme inhibition, as well as the number of enzyme turnovers completed before inhibition, on the concentrations of 3-nitropropionate carbanion and succinate are those expected for an active site-directed and irreversible inhibitor. (ii) The inactivated enzyme is not resuscitated by centrifugation and washing of the mitochondria, in contrast to malonate-treated enzyme, and malonate protects against irreversible, inhibition. (iii) The inhibitor species is 3-nitropropionate carbanion and no external nucleophile is required for inhibition. (iv) The respiratory rates, respiratory control ratios, and ADP/O ratios obtained with NAD-linked substrates are unaffected by 3-nitropropionate carbanion. These results show that 3-nitropropionate carbanion is a highly specific, time-dependent, and irreversible inhibitor of succinate dehydrogenase. By analogy with the reaction of nitroethane with D-amino acid oxidase, the data are consistent with the hypothesis that the carbanionic inhibitor forms a covalent N-5 adduct with the active site flavin. However, the precise mechanism of inactivation, as well as mechanistic extrapolations to the oxidation of succinate, must await the elucidation of the structure of the modified enzyme. We can now explain the toxicity of plants such as Indigofera endecaphylla for mammals and fowl as being due to the irreversible blockage of the Krebs cycle by 3-nitropropionate carbanion.

Animals↗
PubMed1977

Application of a solid membrane ion-selective electrode to in vivo measurements.

A solid membrane electrode containing a highly selective ion-complexing agent immobilized in a polymer membrane is applied to measurements in vivo from the surface of an organ. For the measurements reported here, an ion-complexing agent selective for potassium is incorporated in a silicone rubber membrane and applied to measure ion changes in the brain. Comparison is made to the measurements recorded with an ion-selective microelectrode in the cortical tissue. The surface electrode compares favorably with the microelectrode in terms of amplitude of response and response time for the changes seen in the phenomenon of cortical spreading depression of Leao. The methods reported here are amenable to a selection of ion measurements by incorporation of a suitable ion exchanger in a polymer membrane. Extracellular ion activity is monitored in the anesthetized animal by holding the electrode in a balanced suspension which provides a light, flexible contact to the organ of interest. In the unanesthetized animal, when recording from the brain, the electrode is fixed in a skull-implanted cannula.

Animals↗
PubMed1976

In vivo control of mitochondrial enzyme concentrations and activity by oxygen.

Newborn and adult dog heart mitochondria were prepared from animals chronically adjusted to varying arterial oxygen tensions. Similarly, rat liver and heart mitochondria were isolated from animals acutely exposed to lowered inspired oxygen. After isolation, all mitochondrial samples were assayed under normoxic conditions. These experiments illustrated the following effects of oxygen on mitochondrial function: 1) respiratory activity in State 3 or in the uncoupled state increased after hypoxia and decreased after increased in vivo oxygenation; 2) similarly, the turnover of cytochrome oxidase increased in hypoxia and decreased after increased oxygenation; 3) after chronic hypoxia cytochrome oxidase, cytochrome c and b concentrations decreased per miligram of mitochondrial protein; 4) all mitochondrial preparations were well coupled and exhibited normal capabilities to perform oxidative phosphorylation. The data are interpreted to indicate sensitive control of mitochondrial respiratory capacities by oxygen in vivo.

Acid Phosphatase↗