Rat heart gap junctions as disulfide-bonded connexon multimers: their depolymerization and solubilization in deoxycholate

Abstract

Unproteolyzed gap junctions isolated from rat heart and liver were analyzed for the presence of inter-subunit disulfide bonds by sodium dodecylsulfate polyacrylamide gel electrophoresis. Rat cardiac junctions contained multiple disulfide bonds connecting the Mr 47,000 subunits of the same connexon and of different connexons. Inter-subunit disulfide bonds were absent in liver junctions. Unproteolyzed rat heart gap junctions were resistant to deoxycholate in their oxidized state, but dissolved readily in the detergent when the disulfide bonds were cleaved with beta-mercaptoethanol. Disulfide bonding in proteolyzed cardiac junctions was limited to pairs of Mr 29,500 subunits. These junctions were not soluble in deoxycholate even in the presence of beta-mercaptoethanol. These results show that heart and liver junctions differ in their quarternary organization.