P-type (or E1-E2-type) ATPases constitute a superfamily of cation transport enzymes, present both in prokaryota and eukaryota, whose members mediate membrane flux of all common biologically relevant cations. The ATPases, that form an aspartyl phosphate intermediate in the course of ATP hydrolysis, can be divided into 4 major groups:
(1) Ca2+-transporting ATPases;
(2) Na+/K+- and gastric H+/K+-transporting ATPases;
(3) Plasma membrane H+-transporting ATPases (proton pumps) of plants, fungi and lower eukaryotes; and
(4) all bacterial P-type ATPases, except the Mg2+-ATPase of Salmonella typhimurium, which is more similar to the eukaryotic sequences.