Alterations in number and activity of cerebral free and membrane-bound ribosomes after prolonged ethanol ingestion by the weanling rat

Abstract

Protein synthesis in vitro was studied with free and membrane-bound ribosomes from brain cortices of rats fed for 14 days on a liquid diet containing 6.0% (w/v) ethanol. Free ribosomes from ethanol-fed rats showed an increased ability to incorporate labelled amino acids into protein as compared with the control preparation. The stimulatory effect of ethanol consumption on the protein synthetic activity of free ribosomes was amplified when phenylalanyl-transfer-RNA was used for incorporation studies. Membrane-bound ribosomes from ethanol-treated animals were significantly inhibited in their protein synthetic activity; this effect could be abolished by removal of the membrane with Triton X-100. Ethanol intake resulted in a decline in the aminoacylation of transfer-RNA in the pH 5 enzyme fraction. There was no significant change in the activity of ribonuclease in the postmitochondrial supernatant fraction as a result of ethanol administration. When the control and ‘ethanol’ ribosomes were compared in the peptidyltransferase assay, the activities of both free and membrane-bound ribosomes were found to be stimulated as a consequence of ethanol treatment. It is concluded that the main factors contributing toward the observed stimulation of protein synthesis on cerebral free ribosomes from ethanol-fed rats may be an increased ability of the ‘ethanol’ preparation to transfer the peptidyl group on the ribosome, and a greater amount of ribosome-associated messenger-RNA. The decline in protein synthesis by membrane-bound ribosomes from ethanol-fed rats is attributed to a lesion produced on the endoplasmic reticulum membrane.