Quantification of fatty acid activation of the uncoupling protein in brown adipocytes and mitochondria from the guinea‐pig

Abstract

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, parallelling 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. Copyright © 1986, Wiley Blackwell. All rights reserved