Activating omega-6 polyunsaturated fatty acids and inhibitory purine nucleotides are high affinity ligands for novel mitochondrial uncoupling proteins UCP2 and UCP3.
UCP2 (the lowest Km values: 20 and 29 microm, respectively) for omega-6 polyunsaturated FAs (PUFAs), all-cis-8,11,14-eicosatrienoic and all-cis-6,9,12-octadecatrienoic acids, which are also the most potent agonists of the nuclear PPARbeta receptor in the activation of UCP2 transcription. omega-3 PUFA, cis-5,8,11,14,17-eicosapentaenoic acid had lower affinity (Km, 50 microm), although as an omega-6 PUFA, arachidonic acid exhibited the same low affinity as lauric acid (Km, approximately 200 microm). These findings suggest a possible dual role of some PUFAs in activating both UCPn expression and uncoupling activity. UCP2 (UCP3)-dependent H+ translocation activated by all tested FAs was inhibited by purine nucleotides with apparent affinity to UCP2 (reciprocal Ki) decreasing in order: ADP > ATP approximately GTP > GDP >> AMP. Also [3H]GTP ([3H]ATP) binding to isolated Escherichia coli (Kd, approximately 5 microm) or yeast-expressed UCP2 (Kd, approximately 1.5 microm) or UCP3 exhibited high affinity, similar to UCP1. The estimated number of [3H]GTP high affinity (Kd, <0.4 microm) binding sites was (in pmol/mg of protein) 182 in lung mitochondria, 74 in kidney, 28 in skeletal muscle, and approximately 20 in liver mitochondria. We conclude that purine nucleotides must be the physiological inhibitors of UCPn-mediated uncoupling in vivo.
Zackova
Markéta
M
Institute of Physiology, Academy of Sciences of the Czech Republic, Vídenská 1083, 14220 Prague 4, Czech Republic.
Skobisová
Eva
E
Urbánková
Eva
E
Jezek
Petr
P
D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D003067:Coenzymes; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated / Q000378:metabolism* / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007473:Ion Channels; D007700:Kinetics; D007850:Lauric Acids / Q000494:pharmacology; D008024:Ligands; D008081:Liposomes / Q000378:metabolism; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D011506:Proteins / Q000378:metabolism*; D011522:Protons; D014316:Tritium; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000494:pharmacology; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3; D015003:Yeasts
D002352:Carrier Proteins; D003067:Coenzymes; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D007473:Ion Channels; D007850:Lauric Acids; D008024:Ligands; D008081:Liposomes; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D011522:Protons; C000604389:UCP2 protein, human; C000604392:UCP3 protein, human; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3; D014316:Tritium; C030358:lauric acid; D014451:Ubiquinone; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; C024989:coenzyme Q10