Electrophoretic Studies of the Proteins of Rat Liver Endoplasmic Reticulum

Abstract

The proteins of rough and smooth endoplasmic reticulum of rat liver were examined by electrophoresis in (1) a starch – urea – aluminum lactate system, which resolved 10 components; (2) a starch – urea – aluminum lactate – mercaptoethanol system which resolved 18 components; and (3) a polyacrylamide – sodium dodecyl sulfate (SDS) – urea – mercaptoethanol system, which resolved 33–34 components. In each system, the protein patterns of the membranes of the rough and smooth endoplasmic reticulum were found to be very similar. However, using polyacrylamide–SDS the rough endoplasmic reticulum was found to contain a protein of molecular weight 36 000, which was barely detectable in the smooth endoplasmic reticulum. Evidence is presented which suggests that this was a membrane component, although the possibility that it was a ribosomal protein could not be absolutely excluded. The membranes of the endoplasmic reticulum of male rats were also found to contain a protein of molecular weight 35 000, which was barely detectable in membranes from female rats.