The Na+/K+ ATPase (NKA) enzyme contains α, β and γ subunits. This enzyme is widely expressed. ATPase Na+/K+ transporting subunit α 1 (ATP1A1) is a principal catalytic subunit of NKA. It has a molecular mass of about 110kDa with 10 transmembrane segments. α-subunit has four different isoforms with tissue specific expression. α1 is primarily expressed in various tissues, including kidney, nerves and lung. While α2 is expressed in skeletal muscle and heart, α3 is found in the brain and α4 is apparently localized to testis and specifically to spermatozoa. ATP1A1 is encoded by the gene mapped to human chromosome 1p13-p11.
The sodium/potassium ATPase is an integral membrane enzyme found in all cells of higher organisms and is responsible for the ATP-dependent transport of sodium and potassium across the cell membrane. This membrane-bound enzyme is related to a number of other ATPases including sarcoplasmic and endoplasmic reticulum calcium ATPase (SERCA) and plasma membrane calcium ATPase (PMCA). The sodium/potassium ATPase consists of a large, multipass, transmembrane catalytic subunit, termed the α subunit, and an associated smaller glycoprotein, termed the β subunit. Studies indicate that there are three isoforms of the α subunit (α 1, α 2, α 3) and two isoforms of the β subunit (β 1 and β 2) encoded by two multigene families. The different isoforms of the sodium/potassium ATPase exhibit tissue-specific and developmental patterns of expression. The α 1 and β mRNAs are present in all cell types examined, whereas the α 2 and α 3 mRNAs exhibit a more restricted pattern of cell-specific expression. The α subunit has been found in kidney, brain, heart, and to a lesser extent liver, skeletal and smooth muscle.
