Uncoupling protein--a useful energy dissipator.

The structure/function relationship in the uncoupling proteins (UCP) is reviewed, stressing UCP from brown adipose tissue (UCP1) since, so far, nearly no biochemistry is known for the UCP variants UCP2, UCP3, and UCP4. The transport for H+ and Cl- and its dependence on fatty acids in reconstituted vesicles is described. The inhibition and binding of nucleotides to UCP1, in particular, the pH dependence and two-stage binding are analyzed. A model for the role of fatty acid in H+ transport is shown. The role of specific residues in UCP1 is analyzed by directed mutagenesis in a yeast expression system. The different regulation by the cellular energy potential of UCP1 versus UCP3 is discussed.