Topology of Na+,K+‐ATPase Identification of the extra‐ and intracellular hydrophilic loops of the catalytic subunit by specific antibodies

Abstract

To study the topology of Na+,K+-ATPase monoclonal antibodies (MAbs) specific for membrane-bound enzyme were produced. Using immunofluorescence staining of viable cells or smears of a pig kidney embryonic (PKE) cell line, two groups of MAbs were selected, namely those binding to extra- or intracellular portions of the α-subunit. The extracellular location of peptide loop 804–841 linking the Vth and VIth intramembrane hydrophobic segments was proved using MAb VG2. Another MAb, IIC9, interacting with PKE cells only after membrane perforation (4% formaldehyde and 0.1% Tween-20), was shown to bind to the hydrophilic loop 868–945. The antigenic determinants recognized by MAb IIC9 and VG2 are located in peptides 887–904 and 810–825, respectively. The C-terminus of the α-subunit molecule was positioned on the outer side of the cytoplasmic membrane utilizing affinity-purified antibodies to the synthetic peptide corresponding to fragment 999–1008