The physiological role of the novel uncoupling proteins: view from the chair

The recently cloned uncoupling proteins -2 and -3 (UCP2, UCP3) cDNAs encode for proteins with 57-59% homology with brown adipose tissue uncoupling protein (UCP1) that can function as uncouplers of phosphorylation. The presentations of this Session of the Symposium were largely based on mRNA measurements, with one study showing that protein concentrations are well predicted by changes in mRNA in human muscles. Overall the observations suggest more complexity than anticipated. These observations are for the moment hard to reconcile with a simple role for these proteins in energy dissipation. Just the marked differences in tissue distribution of the two novel UCPs suggest they have different functions. It is possible that the activity, rather than the concentrations of these proteins, is regulated. The investigation of this possibility will hopefully enlighten us on their physiological role.