Comparative analysis of the major polypeptides from liver gap junctions and lens fiber junctions.

Abstract

Gap junctions from rat liver and fiber junctions from bovine lens have similar septilaminar profiles when examined by thin-section EM and differ only slightly with respect to the packing of intramembrane particles in freeze-fracture images. These similarities have often led to lens fiber junctions being referred to as gap junctions. Junctions from both sources were isolated as enriched subcellular fractions and their major polypeptide components compared biochemically and immunochemically. The major liver gap junction polypeptide has an apparent MW of 27,000, while a 25,000-dalton polypeptide is the major component of lens fiber junctions. The 2 polypeptides are not homologous when compared by partial peptide mapping in SDS [sodium dodecyl sulfate]. There is no detectable antigenic similarity between the 2 polypeptides by immunochemical criteria using antibodies to the 25,000-dalton lens fiber junction polypeptide. In spite of the ultrastructural similarities, the gap junction and the lens fiber junction are comprised of distinctly different polypeptides, suggesting that the lens fiber junction contains a unique gene product and potentially different physiological properties.