Comparison of the porcine (Po-), human (Hu-), murine (Mu-), bovine (Bo-) and ovine (Ov-) α subunits amino acids sequences. Black column with white letter, dark gray column with white letter and light gray column with black letter represent identity among 5, 4 and 3 species, respectively. Cysteine residues (¤), potential N-glycosylation sites (#) and potential cytoplasmic-tail phosphorylation sites (+) are marked at the bottom of the sequences. The important Glu-333 residue (E) and the Gln-744 residue (Q) are respectively identified by ($) and (=). The stripes above the sequences represent the deduced different constitutive parts of the protein: signal peptide (), extracellular domain (), transmembrane region (), cytoplasmic tail (),αI-domain () and its metal-ion dependent adhesion site (), and the central divalent cation-binding motifs of the three COOH-terminal repeats (). The highly conserved "GFFKR" motif of the cytoplasmic tail is framed for the different species.