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M Desautels

Publications and source records attributed to M Desautels.

46 records · Page 3Linked to original sources
PubMed1982

Liver mitochondria contain an ATP-dependent, vanadate-sensitive pathway for the degradation of proteins.

A large fraction (30-50%) of the various proteins synthesized within isolated rat liver mitochondria were degraded to amino acids within 60 min after synthesis. Incomplete mitochondrial polypeptides resulting from the incorporation of puromycin were degraded even more extensively (80% per hr). Protein breakdown was measured by the appearance of acid-soluble radioactivity and by the disappearance of labeled polypeptides detected on NaDodSO4/polyacrylamide gel electrophoresis. The amino acids generated by proteolysis were transported rapidly out of the mitochondria and no peptide intermediates accumulated in the organelle. This degradative process did not involve lysosomes or lysosomal enzymes and was markedly stimulated by ATP either generated within the mitochondria or supplied exogenously. An inhibitor of respiration (cyanide) or uncouplers of oxidative phosphorylation (oligomycin, dinitrophenol) reduced proteolysis when mitochondria were provided substrates for ATP generation. When exogenous ATP was provided, these agents did not affect proteolysis, but degradation was then sensitive to atractyloside, an inhibitor of adenine nucleotide transport. Vanadate, an inhibitor of various ATPases, blocked proteolysis even in the presence of ATP and caused a marked stabilization of nearly all polypeptide bands. Thus, mitochondria--like bacteria or the cytosol of animal cells--contain a pathway for complete degradation of proteins which seems to selectively remove polypeptides with abnormal structures. Within this organelle, ATP hydrolysis appears necessary for an initial step in this degradative process.

ATP-Dependent Proteases↗
PubMed1980

Parallel regression of cold-induced changes in ultrastructure, composition, and properties of brown adipose tissue mitochondria during recovery of rats from acclimation to cold.

When cold-acclimated rats are returned to a thermoneutral environment (28 degrees C) after 5 weeks at 4 degrees C, the size of the enlarged interscapular brown adipose tissue decreases during the 1st week. The altered composition of the mitochondria, however, reverts to normal during deacclimation more rapidly than the size of the tissue: a marked decrease in binding of purine nucleotides occurs by 3 days and a decrease in the proportion of polypeptides of molecular weight 25 000-35 000 occurs by 1 day. The very rapid decrease in the polypeptides, compared with the slower decrease in binding of purine nucleotides, known to be to a 32 000 polypeptide, suggests an initial conversion of masked binding sites to another form. Mitochondria isolated from cold-acclimated rats are larger than those of warm-acclimated rats, a difference which appears slowly during acclimation to cold, requiring 7-14 days for full development; during deacclimation the increase in size disappears by 7 days. The ultrastructure of mitochondria isolated from cold-acclimated rats shows inmerices arranged in numerous, narrow, interconnecting parallel sheets in contrast to the sparser broad tubes and bands in mitochondria isolated from warm-acclimated rats. This difference in ultrastructure develops in a biphasic manner during acclimation to cold: an initial appearance (1-12 h) of the parallel arrangement, associated with a transient increase in size, is no longer apparent at 1-3 days and reappears only after 7-14 days. During deacclimation the reversal to the tubular form requires approximately 7 days. During deacclimation the changes in brown adipose tissue mitochondrial composition, structure, size, and properties and in tissue size appear to occur independently.

Acclimatization↗
PubMed1978

Thermogenic mechanisms and their control.

The alterations in properties of mitochondria and of plasma membrane of brown adipose tissue and skeletal muscle of cold-acclimated rats are reviewed in order to bring out any adaptive changes which are related to the mechanism of nonshivering thermogenesis, and thus to the enhanced calorigenic action of catecholamines known to exist in these animals. Since prevention of the morphological changes in the mitochondria by treatment of the animals with oxytetracycline during acclimation to cold also prevents the development of the enhanced calorigenic response to the catecholamines it is concluded that the changes noted are either a cause of the development of the increased capacity for nonshivering thermogenesis during acclimation to cold or are secondary to the operation of nonshivering thermogenesis.

Acclimatization↗
PubMed1978

Increased purine nucleotide binding, altered polypeptide composition, and thermogenesis in brown adipose tissue mitochondria of cold-acclimated rats.

Rapid increases in atractyloside-insensitive binding of purine nucleotides (ADP or GDP) and in a polypeptide of 32 000 occur in brown adipose tissue mitochondria of the rat during acclimation to cold. The increased binding is apparent within 1 h and reaches a maximum after 3--7 days of exposure to 4 degrees C. The increase in the 32 000 peptide occurs more slowly and reaches a maximum after 2--3 weeks. There is a simultaneous decrease in a polypeptide of 96 000, apparent after 1 day and reaching a maximum after 1--2 weeks. Results are interpreted in terms of the appearance of an increased amount of the purine nucleotide-sensitive proton conductance pathway in association with the development of an enhanced thermogenic capacity of brown adipose tissue mitochondria during acclimation of the rat to cold.

Acclimatization↗
PubMedDate not supplied

Temperature and phenylmethylsulfonyl fluoride sensitive loss of uncoupling protein in isolated brown adipose tissue mitochondrial membranes.

When a membrane suspension prepared from isolated rat brown fat mitochondria was incubated at 37 degrees C for 4 h, a loss of uncoupling protein (UCP) immunoreactivity was observed on Western blots. Analysis of [3H]GDP-binding characteristics to UCP in isolated membranes also showed a significant reduction in Bmax without significant effect on Kd. The loss of UCP was not due to protease contamination from lysosomes or mast cell granules, since loss of UCP was still observed when mitochondria were treated with digitonin to lyse lysosomes prior to membrane preparation and when mitochondria were isolated from rats injected with compound 48/80 to degranulate mast cells. Furthermore, loss of UCP was observed at alkaline pH and was not affected by inhibitors of lysosomal enzymes. Loss of UCP immunoreactivity was markedly reduced when membranes were incubated at 4 degrees C or in the presence of phenylmethylsulfonyl fluoride, but was not influenced by the addition of GDP. Overall, these results indicate the presence of a serine protease within brown fat mitochondrial membranes that may be involved in the breakdown of UCP.

Adipose Tissue, Brown↗