Abstract
Based on criteria such as the ADP/O ratio and respiratory control by ADP, the energy-coupling efficiency of brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions for a long time decreased remarkably.The presence of bovine serum albumin, GTP, or ATP plus carnitine in the reaction medium markedly increased the efficiency of oxidative phosphorylation of brown adipose tissue mitochondria. Pre-treatment of brown adipose tissue mitochondria with 2% bovine serum albumin, GTP, or ATP plus carnitine caused a decrease in the amount of free fatty acids bound to the mitochondria from 13.1 to 7.0, 9.0, or 8.2μg per mg protein, respectively. Removal of the free fatty acids by means of these pre-treatments resulted in restoration of efficient oxidative phosphorylation; there was a correlation between the amount of free fatty acids removed and the degree of recovery in the respiratory control ratio. The elimination of only a frac-tion of the free fatty acids, as little as 4μg per mg protein, was sufficient to ensure respiratory control by ADP.
It appears that the free fatty acids which lie mainly outside the inner mito-chondrial membrane are responsible for the decrease in the efficiency of oxidative phosphorylation in brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions.
