Reconstituted Plant Uncoupling Mitochondrial Protein Allows for Proton Translocation via Fatty Acid Cycling Mechanism

Superoxide Stimulates a Proton Leak in Potato Mitochondria That Is Related to the Activity of Uncoupling Protein

“…However, we have shown that in the presence of exogenous superoxide there is an additional proton leak that is inhibitable by GTP and is specific to UCP. This contrasts with results obtained when a purified potato mitochondria UCP was reconstituted into liposomes (18). In this instance, the purified UCP catalyzed a fatty acid-dependent proton conductance that was inhibitable by nucleotides without any requirement for superoxide.…”

“…Two years later the first plant UCP gene was cloned (StUCP from potato) (12), and since then UCP genes have been identified from Arabidopsis (13,14), skunk cabbage (15), wheat (16), and rice (17). UCP-like activity has been observed in isolated mitochondria from a number of plant species and the potato UCP activity has been purified and its proton transport properties recovered by reconsitution into liposomes (18). Furthermore, reconstitution of the AtUCP1 gene product into liposomes has provided the first link between a plant UCP gene and proton transport activity (19).…”

Specific Sequence Motifs of Mitochondrial Uncoupling Proteins

“…An opposing proposal considers a His pair in the UCP1 sequence 3 His 145 -Leu 146 -His 147 to be a site of H + conduction, and predicts that UCP2 lacking this His pair does not allow for uncoupling, whereas UCP3, having only His 149 , is predictedto be a weak protonophore (24). However, potato PUMP, a product of the StUCP gene (10) that mediates FA-induced uncoupling (21,22), does not contain any His in this part of the sequence (11,12). Moreover, no differences were found in the FA-induced H + conduction between the recombinant UCP2 and UCP3 (13).…”

“…For all UCPs, a FA-cycling mechanism (19) has been proposed to explain their function (7,13,(20)(21)(22) and their character as anion transporters (23). UCPs should allow for the uniport of anionic FAs that, after protonation, return by¯ipping back through the lipid bilayer and carry H + (19).…”

Activating ω-6 Polyunsaturated Fatty Acids and Inhibitory Purine Nucleotides Are High Affinity Ligands for Novel Mitochondrial Uncoupling Proteins UCP2 and UCP3

“…Alternatively, if several proteins exist they have the same orientation. This is feasible because of our high lipid-to-protein ratio, 2 and such observations were made for years with UCP1 or plant UCP not only for SPQ monitoring of H ϩ flux, but also for Cl Ϫ and alkylsulfonate flux (22,23,37,40,47).…”