Nonphosphorylating Respiration of Mitochondria from Brown Adipose Tissue of Rats

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Abstract
Mitochondria from brown adipose tissue of cold-acclimated rats (6°C) oxidize α-ketoglutarate at a rate twice that of controls (26°C). In both groups, however, the phosphorus: oxygen ratio with α-ketoglutarate never exceeded unity, and it is essentially zero with either succinate or α-glycerophosphate. Adenosine triphosphatase activity of these mitochondria is very low and it is not stimulated by 2,4-dinitrophenol. In addition, both respiration and phosphorylation are unaffected by adenosine diphosphate, 2,4-dinitrophenol, bovine serum albumin, or glutathione. Endogenous respiration of tissue slices is not stimulated by 2-4-dinitrophenol. It is suggested that brown fat mitochondria are not capable of oxidative phosphorylation, but do phosphorylate at the substrate level. Since these findings provide an unusual example of electron transport by means of an energetically nonconservative pathway, their significance to thermogenesis by brown adipose tissue is particularly emphasized.