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Characterization of a β Subunit of the Gastric H+/K+ Transporting ATPase
Michael A. Reuben, Linda S. Lasater and George Sachs
Proceedings of the National Academy of Sciences of the United States of America
Vol. 87, No. 17 (Sep., 1990), pp. 6767-6771
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2355381
Page Count: 5
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The catalytic subunit of the H+/K+-transporting ATPase (EC 220.127.116.11) has 62% identity to the α, or catalytic subunit, of the Na+/K+-transporting ATPase (EC 18.104.22.168); however, a homologous β subunit was unknown until recently. Removal of the carbohydrate from purified hog H+/K+ATPase vesicles reveals a 35-kDa peptide that, when fragmented with protease V8, gives sequences homologous to both β1 and β2 subunits of the Na+/K+-ATPase. cDNA clones for a β subunit of the gastric H+/K+-ATPase were isolated from a rabbit stomach cDNA library by using degenerate 17-mer oligonucleotide probes made to the protease V8-treated peptides. An open reading frame (54-926) encodes a predicted 291-amino acid peptide with Mr = 33,320, which exhibits 31% and 44% homologies to the Na+/K+-ATPase β1 and Na+/K+-ATPase β2 proteins, respectively. A Kyte-Doolittle hydropathy plot predicts a single N-terminal transmembrane domain with a small hydrophobic region near the C terminus. The presumed extracytosolic domain contains seven potential N-linked glycosylation sites and six out of nine cysteines. Northern (RNA) blot analysis of stomach RNA with the rabbit H+/K+-ATPase β probe identifies a single mRNA of 1.3-1.5 kilobases, similar in concentration to the α subunit mRNA. The presence of a defined gastric H+/K+-ATPase β subunit extends the homology between H+/K+-ATPase and the Na+/K+-ATPase subclass of phosphoenzyme transport ATPase and distinguishes them from the monomeric Ca2+ and proton pump subclasses.
Proceedings of the National Academy of Sciences of the United States of America © 1990 National Academy of Sciences