title: Are rod outer segment ATP-ase and ATP-synthase activity expression of the same protein?
abstract: Vertebrate retinal rod outer segments (OS) consist of a stack of disks surrounded by the plasma membrane, where phototransduction takes place. Energetic metabolism in rod OS remains obscure. Literature described a so-called Mg(2+)-dependent ATPase activity, while our previous results demonstrated the presence of oxidative phosphorylation (OXPHOS) in OS, sustained by an ATP synthetic activity. Here we propose that the OS ATPase and ATP synthase are the expression of the same protein, i.e., of F1Fo-ATP synthase. Imaging on bovine retinal sections showed that some OXPHOS proteins are expressed in the OS. Biochemical data on bovine purified rod OS, characterized for purity, show an ATP synthase activity, inhibited by classical F1Fo-ATP synthase inhibitors. Moreover, OS possess a pH-dependent ATP hydrolysis, inhibited by pH values below 7, suggestive of the functioning of the inhibitor of F1 (IF1) protein. WB confirmed the presence of IF1 in OS, substantiating the expression of F1Fo ATP synthase in OS. Data suggest that the OS F1Fo ATP synthase is able to hydrolyze or synthesize ATP, depending on in vitro or in vivo conditions and that the role of IF1 would be pivotal in the prevention of the reversal of ATP synthase in OS, for example during hypoxia, granting photoreceptor survival.
authors.affiliation: DIFAR, Università di Genova, Genoa, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Calzia
authors.forename: Simona
authors.initials: S
authors.lastname: Candiani
authors.forename: Greta
authors.initials: G
authors.lastname: Garbarino
authors.forename: Federico
authors.initials: F
authors.lastname: Caicci
authors.forename: Silvia
authors.initials: S
authors.lastname: Ravera
authors.forename: Maurizio
authors.initials: M
authors.lastname: Bruschi
authors.forename: Lucia
authors.initials: L
authors.lastname: Manni
authors.forename: Alessandro
authors.initials: A
authors.lastname: Morelli
authors.forename: Carlo Enrico
authors.initials: CE
authors.lastname: Traverso
authors.forename: Giovanni
authors.initials: G
authors.lastname: Candiano
authors.forename: Carlo
authors.initials: C
authors.lastname: Tacchetti
authors.forename: Isabella
authors.initials: I
authors.lastname: Panfoli
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D005455:Fluorescent Antibody Technique; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008751:Methylene Blue / Q000378:metabolism; D008954:Models, Biological; D010084:Oxidation-Reduction; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D006180:Proton-Translocating ATPases; D008751:Methylene Blue