Uncoupling proteins (UCPs) are molecules that usually generate heat in the mitochondria of brown adipose tissue, but their function in other tissues remains unclear. In 3 January Nature, Karim Echtay and colleagues from the Medical Research Council's Dunn Human Nutrition Unit, Cambridge, UK, show that UCPs may have a role in decreasing reactive oxygen species concentrations inside mitochondria.

Echtay et al. observed that superoxide increases mitochondrial proton conductance through effects on UCP1, UCP2 and UCP3. They showed that superoxide-induced uncoupling requires fatty acids and is inhibited by purine nucleotides. This effect correlates with the tissue expression of UCPs, appears in mitochondria from yeast expressing UCP1 and is absent in skeletal muscle mitochondria from UCP3 knockout mice (Nature 2002, 415:96-99).

"UCP1 evolved a thermogenic role in mammals as a side pathway of an original, more general function of protection against the cold-induced production of reactive oxygen...