Mallo Seijas, NataliaLamas Fernández, JesúsFelipe González, Ana Paula deCastro de Antonio, María Eugenia deSueiro Benavides, Rosa AnaLeiro Vidal, José Manuel2019-01-302019-01-302016-04Mallo N, Lamas J, Defelipe AP, Decastro ME, Sueiro RA, Leiro JM. (2016).Presence of an isoform of H+-pyrophosphatase located in the alveolar sacs of a scuticociliate parasite of turbot: physiological consequences. Parasitology143: 576-87. doi: 10.1017/S00311820150019970031-1820http://hdl.handle.net/10347/18171This article has been published in a revised form in Parasitology [http://doi.org/10.1017/ S0031182015001997]. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works. © 2017 Cambridge University PressH+-pyrophosphatases (H+-PPases) are integral membrane proteins that couple pyrophosphate energy to an electrochemical gradient across biological membranes and promote the acidification of cellular compartments. Eukaryotic organisms, essentially plants and protozoan parasites, contain various types of H+-PPases associated with vacuoles, plasma membrane and acidic Ca+2 storage organelles called acidocalcisomes. We used Lysotracker Red DND-99 staining to identify two acidic cellular compartments in trophozoites of the marine scuticociliate parasite Philasterides dicentrarchi: the phagocytic vacuoles and the alveolar sacs. The membranes of these compartments also contain H+-PPase, which may promote acidification of these cell structures. We also demonstrated for the first time that the P. dicentrarchi H+-PPase has two isoforms: H+-PPase 1 and 2. Isoform 2, which is probably generated by splicing, is located in the membranes of the alveolar sacs and has an amino acid motif recognized by the H+-PPase-specific antibody PABHK. The amino acid sequences of different isolates of this ciliate are highly conserved. Gene and protein expression in this isoform are significantly regulated by variations in salinity, indicating a possible physiological role of this enzyme and the alveolar sacs in osmoregulation and salt tolerance in P. dicentrarchieng© 2017 Cambridge University Press. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative worksH+-PPasePhilasterides dicentrarchiAlveolar sacsOsmoregulationjournal article10.1017/S00311820150019971469-8161open access