Purine Nucleotides Similarly Regulate Uncoupling Protein 3 and 1

Abstract

ATP generation is fueled by an electrical potential across the inner mitochondrial membrane (IMM), which can be decreased by an uncoupling protein (UCP) facilitated proton leak. Apart from UCP1, which supports non-shivering thermogenesis, the function of the other UCPs, such as UCP3, remains unknown. In contrast to UCP1, few results on UCP3 regulation from studies on isolated mitochondria or liposomes imply that ADP/GDP has a stronger inhibitory effect on UCP3 than ATP/GTP. In light of the fact that both, UCP1 and UCP3 were found in brown adipose tissue, we now test whether UCP3 and UCP1 are regulated differently. For this we compare the inhibition of UCP1 and UCP3 by PNs of varying phosphorylation and concentration, using a system of planar bilayers reconstituted with recombinant protein and FAs (1). In contrast to liposomes, this enables us to directly apply the membrane potential necessary for UCP3 function under physiological conditions. These results show that ATP and not ADP is the most potent UCP3 inhibitor and this is likewise similar to UCP1 and UCP2 (2, 3). UCP3 conductance is more strongly inhibited by the same PN concentrations than is UCP1 conductance, and adenosine nucleotides are more effective inhibitors than guanosines. Our results demonstrate that inhibition of UCP3 is similar to that of UCP1. We anticipate these findings as a starting point to examine whether different factors (in comparison to UCP1) are required to activate UCP3.(1) Beck et al. (2006) Biochim Biophys Acta. 1757(5-6):474-9.(2) Beck et al. (2007) FASEB J. 21(4):1137-44.(3) Rupprech et al. (2010) Biophys J. 98(8):1503-11.