Comparison of the protein content of three different bovine secretory granule membrane types: a search for exocytosis-specific shared proteins

A two-dimensional polyacrylamide gel analysis of three types of bovine exocytotic granule membranes has been undertaken. Great care was taken to purify the membranes of biochemical homogeneity with minimal contamination from other membrane sources. The goal was to identify proteins that were present in all three membrane types. Although a number of minor components were observed that co-migrated for two membrane types, no proteins were detected that were present in all three granule membranes. We therefore conclude that such exocytosis- specific proteins do not exist or that they represent less than 0.1% of the total membrane protein present in a given isolated membrane preparation.