Differential interaction of fatty acids and fatty acyl CoA esters with the purified/reconstituted brown adipose tissue mitochondrial uncoupling protein

Proteoliposomes containing highly purified uncoupling protein generated by a modified purification/reconstitution procedure carried out active GDP dependent proton conductance. It was further established that long chain acyl CoA esters as well as fatty acids stimulated proton influx by the uncoupling protein, and, moreover, that the acyl CoA esters were partially effective in overcoming the inhibition by GDP. GDP binding to the purified uncoupling protein was inhibited by acyl CoA esters but not fatty acids. Phenylglyoxal which prevents GDP binding to the uncoupling protein eliminated the acyl CoA but not the fatty acid effect on proton conductance. These results substantiate the fact that nucleotides and acyl CoA esters act at the same regulatory site on the uncoupling protein, whereas, fatty acids act at a separate site. The properties of the purified/reconstituted uncoupling protein confirm they are identical to those inherent in brown adipose tissue mitochondria.