Differences between liver gap junction protein and lens MIP 26 from rat: Implications for tissue specificity of gap junctions

Liver gap junctions and gap-junction-like structures from eye lenses are each comprised of a single major protein (M_r 28,000 and 26,000, respectively). These proteins display different two-dimensional peptide fingerprints, distinct amino acid compositions, nonhomologous N-terminal amino acid sequences and different sensitivities to proteases when part of the intact junction. However, the junctional protein of each tissue is well conserved between species, as demonstrated previously for lens and now for liver in several mammalian species. The possibility of tissue-specific gap junction proteins is discussed in the light of data suggesting that rat heart gap junctions are comprised of yet a third protein.