Immunochemical demonstration of a novel beta-subunit isoform of X, K-ATPase in human skeletal muscle

Abstract

Recently we have identified mRNA encoding a hitherto unknown mammalian X,K-ATPase beta-subunit expressed predominantly in muscle tissue (Pestov, N. B. et al. (1999) FEBS Lett. 456, 243-248). Here we demonstrate the existence of the predicted protein, designated as beta(m) (beta(muscle)), in human adult skeletal muscle membranes using immunoblotting with beta(m)-specific antibodies generated against recombinant polypeptide formed by extramembrane beta(m) domains. The electrophoretic mobility of beta(m) was shown to be abnormally low due to the presence of Glu-rich sequences. In contrast to mature forms of other known X,K-ATPase beta-subunits, carbohydrate moiety of beta(m) is sensitive to endoglycosidase H and appears to be composed of short high-mannose or hybrid N-glycans. This finding argues in favor of an intracellular location of beta(m) in human skeletal muscle.