Functional interaction of free polyribosomes with the membrane of the endoplasmic reticulum in a cell-free protein-synthesizing system from plasmacytoma X5563

In cell-free protein synthesis by the murine plasmacytoma X5563, which had become a nonproducing mutant, mixed systems with free polyribosomes and mirosomes incorporated ¹⁴C-amino-acid into protein 3–8 times greater than the sum of the incorporations in the individual system irrespective of S-100 concentrations. This enhancement was inhibited by lecithinase A and was markedly reduced at high KCl concentrations. Smooth endoplasmic membranes had more stimulatory activity than rough endoplasmic membranes. The results indicate that the membrane of the endoplasmic reticulum and free polyribosomes interact in the cell-free protein-synthesizing system, resulting in the enhancement of protein synthesis.