Hydrogen potassium ATPase

ATPase, H+/K+ exchanging, alpha polypeptide
Identifiers
Symbol	ATP4A
Entrez	495
HUGO	819
OMIM	137216
RefSeq	NM_000704
UniProt	P20648
Other data
EC number	3.6.3.10
Locus	Chr. 19 q13.1

ATPase, H+/K+ exchanging, beta polypeptide
Identifiers
Symbol	ATP4B
Entrez	496
HUGO	820
OMIM	137217
RefSeq	NM_000705
UniProt	P51164
Other data
EC number	3.6.3.10
Locus	Chr. 13 q34

Gastric hydrogen potassium ATPase, also known as H⁺/K⁺ ATPase, is an enzyme which functions to acidify the stomach.

The gastric hydrogen potassium ATPase or H⁺/K⁺ ATPase is the proton pump of the stomach. It exchanges potassium from the intestinal lumen with cytoplasmic hydronium and is the enzyme primarily responsible for the acidification of the stomach contents and the activation of the digestive enzyme pepsin (see gastric acid).

The H⁺/K⁺ ATPase is found in parietal cells, which are highly specialized epithelial cells located in the inner cell lining of the stomach called the gastric mucosa. Parietal cells possess an extensive secretory membrane system and the H⁺/K⁺ ATPase is the major protein constituent of these membranes. A small amount of H⁺/K⁺ ATPase is also found in the renal medulla.

The H⁺/K⁺ ATPase is a heterodimeric protein, the product of 2 genes. The gene ATP4A encodes the H⁺/K⁺ ATPase α subunit, and is an ~1000-amino acid protein that contains the catalytic sites of the enzyme and forms the pore through the cell membrane that allows the transport of ions. Hydronium ions bind to two active sites present in the α subunit. The α subunit also has a phosphorylation site (Asp³⁸⁵). The gene ATP4B encodes the β subunit of the H⁺/K⁺ ATPase, which is an ~300-amino acid protein with a 36-amino acid N-terminal cytoplasmic domain, a single transmembrane domain, and a highly glycosylated extracellular domain.

The H⁺/K⁺ ATPase β subunit stabilizes the H⁺/K⁺ ATPase α subunit and is required for function of the enzyme. The β subunit prevents the pump from running in reverse, and it also appears to contain signals that direct the heterodimer to membrane destinations within the cell, although some of these signals are subordinate to signals found in H⁺/K⁺ ATPase α subunit.

The structure of H⁺/K⁺ ATPase has been determined for humans, dogs, hogs, rats, and rabbits and is 98% homologous across all species.

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