Succinylation of proteins associated with the ribosomal attachment site on microsomal membranes

Ribosome-free membranes, prepared from rat liver endoplasmic reticulum by means of 2M LiCl, lost 90% of their ability to accept ribosomes for reattachment after exposure to succinic anhydride. However, treatment of rough-surfaced endoplasmic reticulum with succinic anhydride, prior to the removal of bound ribosomes by 2M LiCl, gave rise to membranes that were still able to accept ribosomes for reattachment. Succinylation of rough-surfaced endoplasmic reticulum resulted in the removal of some loosely-bound ribosomes and also a slight loss in glucose-6-phosphatase activity. Rough-surfaced endoplasmic reticulum, preincubated with succinic anhydride prior to treatment with lithium chloride, was exposed to [3H]succinic anhydride and subsequently analysed by dodecylsulfate polyacrylamide gel electrophoresis. By this means it was found that there were at least three proteins of different molecular weights that were associated with the membrane ribosomal attachment site.