PRIMARY STRUCTURE AND FUNCTIONAL EXPRESSION OF THE NA/CA,K-EXCHANGER FROM BOVINE ROD PHOTORECEPTORS

Complementary DNA encoding the Na/Ca,K-exchanger was isolated from bovine retina cDNA libraries. The complete full-length cDNA is approximately 4 kb long and contains an open reading frame of 3597 bp. The deduced amino acid sequence corresponds to a protein of 1199 amino acids with a calculated molecular weight of approximately 130 kDa. Hydrophobicity analysis revealed the presence of two alternating sets of hydrophobic and hydrophilic domains. There also exists a hydrophobic region at the N-terminus which may be part of a cleavable signal peptide. The protein shares limited sequence homology with the Na/Ca-exchanger from cardiac sarcolemma. Northern blot analysis indicates that the approximately 6 kb transcript is highly specific for retinal tissue. Insect cells infected with recombinant baculovirus bearing the full-length cDNA express a functional Na/Ca,K-exchanger with an apparent relative molecular weight of approximately 210 kDa, as determined by Western blotting.