Studies on the energy state of isolated brown adipose tissue mitochondria. Effect of adenine nucleotides and oligomycin on the generation and dissipation of the “energy potential”

Energization of isolated brown adipose tissue mitochondria of cold-stressed guinea pigs has been studied by measuring rates and steady-state reduction of the cytochrome b complex. Our previous conclusion (Pedersen, J. I. and Flatmark, T. (1972) Biochim. Biophys. Acta 275, 135–147) that brown adipose tissue and liver mitochondria of these animals are fundamentally different from an energetic point of view, has been confirmed.ADP induced an energization of brown adipose tissue mitochondria very similar to that previously observed with ATP (ref. cited), but the maximal “energy potential” obtained by ADP is lower. Furthermore, this potential of brown adipose tissue mitochondria is much more sensitive to changes in the extramitochondrial phosphate potential than is that of liver mitochondria. Energization by ADP is largely mediated by ATP formed by the adenylate kinase reaction.The oligomycin-induced oxidation of the cytochrome b complex of maximally energized mitochondria appears to be a suitable measure of the rate of energy dissipation. By using this parameter, it has been found that the rate as well as the extent of endogenous dissipation of energy is approx. 15 times higher in brown adipose tissue mitochondria than in liver mitochondria at pH 6.8. The pH dependence of this reaction is a further indication of the importance of the transmembrane pH gradient in the control of coupling of electron transport to phosphorylation in brown adipose tissue mitochondria.