Catalytic subunit isoforms of mammalian lens Na, K-ATPase

Abstract

To identify the Na, K-ATPase isoforms present in the mammalian lens, seven antisera were prepared to selected peptide sequences of the catalytic (α) subunit. Three antisera were prepared to peptide sequences at the N-terminus of the three sequenced rat α isoforms. There is < 53% sequence homology among the isoforms in this region. Three antisera were prepared to peptide sequences at the ouabain binding site in the extracellular loop between membrane spanning sequences 1 and 2 of the sequenced rat a isoforms; sequence homology among the isoforms in this region is < 69%. An antiserum was also prepared to the carboxyl terminal region of the α2 rat isoform. The sequenced isoforms (rat and human) in this region are < 94% homologous. The results from stains of Western blots of SDS-PAGE separations of lens membranes are presented, α1 is the predominant isoform of the epithelium. It is not found in cells of the central epithelium but is present in cells located more toward the equator. α3 is the catalytic subunit of the central 43% of the epithelium. The lens fiber cell membranes have a catalytic subunit that is related to the α2 isoform. In the fiber cell a 98–100 kDa band stains with the antiserum to the α2 N-terminus and the antiserum to the α2 ouabain site. The antiserum to the α2 C-terminus does not stain the 98–100 kDa band. (Preliminary reports of these results were presented at the 1992 and 1993 meetings of the Association for Research in Vision and Ophthalmology).