Identification of a novel gene of the X,K‐ATPase β‐subunit family that is predominantly expressed in skeletal and heart muscles1

Abstract
We have identified the fifth member of the mammalian X,K-ATPase β-subunit gene family. The human and rat genes are largely expressed in skeletal muscle and at a lower level in heart. The deduced human and rat proteins designated as βmusclem) consist of 357 and 356 amino acid residues, respectively, and exhibit 89% identity. The sequence homology of βm proteins with known Na,K- and H,K-ATPase β-subunits are 30.5–39.4%. Unlike other β-subunits, putative βm proteins have large N-terminal cytoplasmic domains containing long Glu-rich sequences. The data obtained indicate the existence of hitherto unknown X,K-ATPase (most probably Na,K-ATPase) isozymes in muscle cells.