UCP1, UCP2 and UCP3: Are they true uncouplers of respiration?

The thermogenesis in brown adipose tissue (BAT) is due to the activity of a mitochondrial uncoupling protein (UCP1). This protein allows the protons p umped by the respiratory chain to re-enter the matrix without ATP synthesis . Therefore respiration is dramatically increased and produces only heat. T he discovery of genes showing strong similarities with the UCP1 gene and ex pressed in other tissues raised the possibility that these proteins partici pate in the proton leak observed in mitochondria, and therefore participate in the regulation of energy expenditure. The recombinant expression of UCP 1. UCP2 and UCP3 in yeast allows the comparison of the coupling state of ye ast mitochondria in the presence or absence of these proteins.