Independent lines of evidence suggesting a major gap junctional protein with a molecular weight of 26,000.

Several polypeptides have been described in the past as components of gap junction fractions. Of these, a peptide of Mr 26,000 is found in gap junctions isolated from livers of different species under conditions that minimize proteolysis. Tryptic digestion of purified "intact" junctions causes the rapid disappearance of this peptide with a concomitant appearance of a band of Mr 10,000, which has previously been found to be characteristic of junctional fractions isolated with the aid of proteolytic treatment. Both the peptides of Mr 26,000 and 10,000 are missing from gap junction preparations after partial hepatectomy, when gap junctions are absent from the surface of the hepatocytes. They have reappeared in fractions from the livers of animals killed 3 days postoperatively, when gap junctions are again present in vivo.