The possible proton translocating activity of the mitochondrial uncoupling protein of brown adipose tissue

Myopathic Syrian hamsters (BIO 14.6) have less brown adipose tissue (BAT) than normal. The trophic response of this tissue to cold is smaller than normal and trophic responses to diet and to photoperiod are absent. The objective was to find out whether activity of thyroxine 5'-deiodinase in their BAT was increased normally in response to cold and thus whether a defect in endogenous production of 3,5,3'-triiodothyronine might underlie the attenuated trophic response. The effect of feeding a high-fat diet on activity of 5'-deiodinase was also studied. Cold acclimation increased thyroxine 5'-deiodinase activity in BAT of the myopathic hamster, but the total remained smaller than normal because of the smaller size. The cold-induced increase in concentration of mitochondrial uncoupling protein was also smaller than normal. The level of serum 3,5,3'-triiodothyronine was low in myopathic hamsters and remained lower than normal when they were cold-exposed or cold acclimated. Feeding the high-fat diet to myopathic hamsters resulted in a greater than normal suppression of thyroxine 5'-deiodinase activity than in normal hamsters; the normal increases in protein content and in concentration of mitochondrial uncoupling protein were absent. We conclude that the defective trophic response of BAT of the myopathic hamster is not secondary to defective regulation of its thyroxine 5'-deiodinase activity because this activity does not appear to be obligatorily linked to hypertrophy of BAT. The low level of serum 3,5,3'-triiodothyronine in the myopathic hamster may be secondary to reduced capacity for peripheral thyroxine deiodination in its BAT.

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Measurement by radioimmunoassay of the mitochondrial uncoupling protein from brown adipose tissue of obese (ob/ob) mice and Zucker (fa/fa) rats at different ages

FEBS Letters ◽

10.1016/0014-5793(85)80525-1 ◽

1985 ◽

Vol 179 (2) ◽

pp. 233-237 ◽

Cited By ~ 26

Author(s):

Margaret Ashwell ◽

Susan Holt ◽

Graham Jennings ◽

Dorothy M. Stirling ◽

Paul Trayhurn ◽

...

Keyword(s):

Adipose Tissue ◽

Brown Adipose Tissue ◽

Uncoupling Protein ◽

Mitochondrial Uncoupling ◽

Mitochondrial Uncoupling Protein ◽

Brown Adipose ◽

Different Ages

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Regulation of GDP binding and uncoupling-protein concentration in brown-adipose-tissue mitochondria. The effects of cold-acclimation, warm-reacclimation and noradrenaline

Biochemical Journal ◽

10.1042/bj2490451 ◽

1988 ◽

Vol 249 (2) ◽

pp. 451-457 ◽

Cited By ~ 27

Author(s):

T Peachey ◽

R R French ◽

D A York

Keyword(s):

Adipose Tissue ◽

Brown Adipose Tissue ◽

Protein Concentration ◽

Uncoupling Protein ◽

Potassium Acetate ◽

Zucker Rats ◽

Mitochondrial Uncoupling ◽

Mitochondrial Uncoupling Protein ◽

Acute Response ◽

Brown Adipose

We have used a specific immunoassay for uncoupling protein and [3H]GDP binding to study the acute and chronic responses of brown-adipose-tissue (BAT) mitochondria of warm-acclimated rats to housing at 4 degrees C and cold-acclimated rats to housing at 27 degrees C. These studies have shown the following. (1) In the cold-exposed rat the increase in mitochondrial uncoupling-protein concentration parallels the increase in GDP binding from 1 day to 5 days, but that acutely (initial 4 h) the increase in GDP binding is not associated with any change in uncoupling-protein concentration. 2. In the cold-acclimated rat rehoused at 27 degrees C, GDP binding fell by over 50% in the first 2 days, without any change in uncoupling-protein concentrations. 3. Noradrenaline acutely (30 min) increased BAT mitochondrial GDP binding of lean and obese Zucker rats, without any change in uncoupling-protein concentrations. 4. The increases in GDP binding in cold-exposed rats were associated with increases in the rate of swelling of mitochondria in the presence of valinomycin and potassium acetate. The evidence supports the hypothesis that the acute response of the rat to changes in environmental temperature are associated with unmasking or remasking of uncoupling protein, whereas chronically changes in uncoupling-protein concentration predominate.

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Immunochemical detection and quantitation of brown adipose tissue uncoupling protein

Biochemistry and Cell Biology ◽

10.1139/o87-032 ◽

1987 ◽

Vol 65 (3) ◽

pp. 245-251 ◽

Cited By ~ 9

Author(s):

Mary F. Henningfield ◽

Robert W. Swick

Keyword(s):

Adipose Tissue ◽

Brown Adipose Tissue ◽

Uncoupling Protein ◽

Mammalian Species ◽

Sodium Dodecyl ◽

Mitochondrial Uncoupling ◽

Immunochemical Method ◽

Nucleotide Binding Sites ◽

Mitochondrial Uncoupling Protein ◽

Brown Adipose

A polyclonal antisera against rat brown adipose tissue mitochondrial uncoupling protein was used to examine mitochondrial samples from liver and white and brown adipose tissue from several mammalian species. A sodium dodecyl sulfate – polyacrylamide gel electrophoretic separation of proteins combined with an immunochemical method allowed for visualization of antigen–antibody complexes on nitrocellulose blots. Hamster, cavy, monkey, and mouse brown adipose tissue mitochondrial samples cross-reacted with the antisera. Mitochondria prepared from white fat obtained from young swine and sheep contained two closely migrating, antigenically active proteins. Hepatic mitochondria samples did not contain antigenically active protein. Reflectance densitometry was used for quantitation of the uncoupling protein in various mitochondrial samples. In rats fed diets low in protein, there appears to be a dissociation between the concentration of uncoupling protein and the number of nucleotide binding sites as given by the [3H]GDP binding assay. These results are indicative of a physiological activation of the uncoupling protein.

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Mitochondrial uncoupling protein may participate in futile cycling of pyruvate and other monocarboxylates

AJP Cell Physiology ◽

10.1152/ajpcell.1998.275.2.c496 ◽

1998 ◽

Vol 275 (2) ◽

pp. C496-C504 ◽

Cited By ~ 26

Author(s):

Petr Jezek ◽

Jirí Borecky

Keyword(s):

Fatty Acids ◽

Adipose Tissue ◽

Brown Adipose Tissue ◽

Uncoupling Protein ◽

Specific Inhibitor ◽

Physiological Role ◽

Mitochondrial Uncoupling ◽

Mitochondrial Uncoupling Protein ◽

Brown Adipose ◽

Futile Cycling

The physiological role of monocarboxylate transport in brown adipose tissue mitochondria has been reevaluated. We studied pyruvate, α-ketoisovalerate, α-ketoisocaproate, and phenylpyruvate uniport via the uncoupling protein (UCP1) as a GDP-sensitive swelling in K+ salts induced by valinomycin or by monensin and carbonyl cyanide- p-(trifluoromethoxy)phenylhydrazone in Na+ salts. We have demonstrated that this uniport is inhibited by fatty acids. GDP inhibition in K+ salts was not abolished by an uncoupler, indicating a negligible monocarboxylic acid penetration via the lipid bilayer. In contrast, the electroneutral pyruvate uptake (swelling in ammonium pyruvate or potassium pyruvate induced by change in pH) mediated by the pyruvate carrier was inhibited by its specific inhibitor α-cyano-4-hydroxycinnamate but not by fatty acids. Moreover, α-cyano-4-hydroxycinnamate enhanced the energization of brown adipose tissue mitochondria, which was monitored fluorometrically by 2-(4-dimethylaminostyryl)-1-methylpyridinium iodide and safranin O. Consequently, we suggest that UCP1 might participate in futile cycling of unipolar ketocarboxylates under certain physiological conditions while expelling these anions from the matrix. The cycle is completed on their return via the pyruvate carrier in an H+ symport mode.

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