Natural and Azido Fatty Acids Inhibit Phosphate Transport and Activate Fatty Acid Anion Uniport Mediated by the Mitochondrial Phosphate Carrier

The electroneutral Pi uptake via the phosphate carrier (PIC) in rat liver and heart mitochondria is inhibited by fatty acids (FAs), by 12-(4-azido-2-nitrophenylamino)dodecanoic acid (AzDA) and heptylbenzoic acid (∼1 μm doses) and by lauric, palmitic, or 12-azidododecanoic acids (∼0.1 mmdoses). In turn, reconstituted E. coli-expressed yeast PIC mediated anionic FA uniport with a similar pattern leading to FA cycling and H+ uniport. The kinetics of Pi/Pi exchange on recombinant PIC in the presence of AzDA better corresponded to a competitive inhibition mechanism. Methanephosphonate was identified as a new PIC substrate. Decanephosphonate, butanephosphonate, 4-nitrophenylphosphate, and other Pi analogs were not translocated and did not inhibit Pi transport. However, methylenediphosphonate and iminodi(methylenephosphonate) inhibited both electroneutral Pi uptake and FA cycling via PIC. AzDA analog 16-(4-azido-2-nitrophenylamino)-[3H4]-hexadecanoic acid (3H-AzHA) bound upon photoactivation to several mitochondrial proteins, including the 30- and 34-kDa bands. The latter was ascribed to PIC due to its specific elution pattern on Blue Sepharose and Affi-Gel. 3H-AzHA photolabeling of recombinant PIC was prevented by methanephosphonate and diphosphonates and after premodification with 4-azido-2-nitrophenylphosphate. Hence, the demonstrated PIC interaction with monovalent long-chain FA anions, but with divalent phosphonates of short chain only, indicates a pattern distinct from that valid for the mitochondrial uncoupling protein-1.