In the gills of rainbow trout and Atlantic salmon, the α1a- and α1b-isoforms of Na,K-ATPase are expressed reciprocally during salt acclimation. The α1a-isoform is important for Na+ uptake in freshwater, but the molecular basis for the functional differences between the two isoforms is not known. Here, three amino acid substitutions are identified in transmembrane segment 5 (TM5), TM8 and TM9 of the α1a-isoform compared to the α1b-isoform, and the functional consequences are examined by mutagenesis and molecular modeling on the crystal structures of Ca-ATPase or porcine kidney Na,K-ATPase. In TM5 of the α1a-isoform, a lysine substitution, Asn783 → Lys, inserts the ε-amino group in cation site 1 in the E1 form to reduce the Na+/ATP ratio. In the E2 form the ε-amino group approaches cation site 2 to force ejection of Na+ to the blood phase and to interfere with binding of K+. In TM8, a Asp933 → Val substitution further reduces K+ binding, while a Glu961 → Ser substitution in TM9 can prevent interaction of FXYD peptides with TM9 and alter Na+ or K+ affinities. Together, the three substitutions in the α1a-isoform of Na,K-ATPase act to promote binding of Na+ over K+ from the cytoplasm, to reduce the Na+/ATP ratio and the work done in one Na,K pump cycle of active Na+ transport against the steep gradient from freshwater (10–100 μm Na+) to blood (160 mm Na+) and to inhibit binding of K+ to allow Na+/H+ rather than Na+/K+ exchange.
The Journal of Membrane Biology – Springer Journals
Published: Jun 25, 2008
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera