Decoupling the Na+-K+-ATPase in vivo: a possible new role in the gills of freshwater fishes.
The literature suggests that when Na(+)-K(+)-ATPase has reduced access to its glycosphingolipid cofactor sulfogalactosyl ceramide (SGC), it is converted to a Na(+) uniporter. We recently showed that such segregation can occur within a single membrane when Na(+)-K(+)-ATPase is excluded from membrane microdomains or 'lipid rafts' enriched in SGC (D. Lingwood, G. Harauz, J.S. Ballantyne, J. Biol. Chem. 280, 36545-36550). Specifically we demonstrated that Na(+)-K(+)-ATPase localizes to SGC-enriched rafts in the gill basolateral membrane (BLM) of rainbow trout exposed to seawater (SW) but not freshwater (FW). We therefore proposed that since the freshwater gill Na(+)-K(+)-ATPase was separated from BLM SGC it should also transport Na(+) only, suggesting a new role for the pump in this epithelium. In this paper we discuss the biochemical evidence for SGC-based modulation of transport stoichiometry and highlight how a unique asparagine-lysine substitution in the FW pump isoform and FW gill transport energetics gear the Na(+)-K(+)-ATPase to perform Na(+) uniport.
Lingwood
D
D
Department of Integrative Biology, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1. lingwood@mpi-cbg.de
Harauz
G
G
Ballantyne
J S
JS
D000595:Amino Acid Sequence; D000818:Animals; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D005699:Galactosylceramides / Q000378:metabolism*; D005880:Gills / Q000201:enzymology*; D008969:Molecular Sequence Data; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000378:metabolism*
D005699:Galactosylceramides; C049408:sulfogalactocerebroside; D000254:Sodium-Potassium-Exchanging ATPase