Mitochondrial proton leak and the uncoupling protein 1 homologues

Mitochondrial proton leak is the largest single contributor to the standard metabolic rate (SMR) of a rat, accounting for about 20% of SMR. Yet the me chanisms by which proton leak occurs are incompletely understood. The avail able evidence suggests that both phospholipids and proteins in the mitochon drial inner membrane are important determinants of proton conductance. The uncoupling protein 1 homologues (e.g. UCP2, UCP3) may play a role in mediat ing proton leak, but it is unlikely they account for all of the observed pr oton conductance. Experimental data regarding the functions of these protei ns include important ambiguities and contradictions which must be addressed before their function can be confirmed. The physiological role of the prot on leak, and of the uncoupling protein 1 homologues, remains similarly uncl ear. (C) 2001 Elsevier Science B.V. All rights reserved.