the interactions of various preparations of endoplasmic reticulum membranes and polysomes have been studied by means of a sandwich sucrose gradient that clearly isolates free ribosomes , smooth endoplasmic reticulum ( s.e.r . ) and rough endoplasmic reticulum ( r.e.r . ) from the microsomal fraction of rat liver homogenates .
C1179933
free ribosomes
C0230779
rough