Uncoupling protein, H+ transport and regulation.

The biochemical functions of uncoupling proteins (UCPs) are discussed with the view of UCP1 as a paradigm. In contrast with UCP1, the heterologous expression of UCP3 in yeast is found to result primarily in extra-mitochondrial deposits and thus is unsuitable for studying UCP3 function. On expression in Escherichia coli inclusion bodies, UCPs extracted and incorporated into vesicles showed no H(+) transport, only Cl(-) transport. Only after addition of coenzyme Q was fully nucleotide-sensitive high-H(+) transport reconstituted, with UCP1 as well as with UCP2 and UCP3. The newly discovered cofactor role of coenzyme Q in H(+) transport is proposed to imply co-operation with fatty acids for the injection of H(+) into the UCP channel.