Quantification of fatty acid activation of the uncoupling protein in brown adipocytes and mitochondria from the guinea-pig.
Brown adipocytes from cold-adapted guinea-pigs (C-cells) are more sensitive to uncoupling by exogenous palmitate than are cells from warm-adapted animals (W-cells) with much less uncoupling protein. Half-maximal respiratory stimulation of C-cells requires 80 nM free palmitate. Noradrenaline-stimulated lipolysis is not rate-limiting for the respiration of either C-cells or W-cells. Half-maximal stimulation of fatty acid oxidation by mitochondria from warm-adapted guinea-pigs (W-mitochondria) and cold-adapted guinea-pigs (C-mitochondria) both require 12 nM free palmitate. Palmitate uncouples C-mitochondria much more readily than M-mitochondria, paralleling its action on the adipocytes. The uncoupling is partially saturable, about 100 nM free palmitate being required for half-maximal response of C-mitochondria. W- and C-mitochondria show identical binding characteristics for palmitate. The respiratory increase of mitochondria is calculated as a function of bound palmitate. After correcting for the residual uncoupling protein present in W-mitochondria, palmitate is estimated to be almost ineffective as an uncoupler of brown fat mitochondria in the absence of the protein. It is concluded that fatty acids display characteristics required of a necessary and sufficient physiological activator of the uncoupling protein.
S A
SA
Cunningham
H
H
Wiesinger
D G
DG
Nicholls
D000222:Adaptation, Physiological; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D006168:Guinea Pigs; D008066:Lipolysis / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000494:pharmacology; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D013696:Temperature
D002352:Carrier Proteins; D005227:Fatty Acids; D010169:Palmitic Acids; D011773:Pyruvates; C030559:uncoupler-binding protein, Bos taurus; D019308:Palmitic Acid; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D019289:Pyruvic Acid; D009638:Norepinephrine