Studies on the Transfer of Incomplete Polypeptide Chains across Rat Liver Microsomal Membranes in Vitro

A rat liver microsomal system in vitro was used to study the transport of protein from the attached ribosomes to the contents of the microsomal vesicle. Puromycin caused a release of the protein from the ribosomes and the released protein was transferred to the contents of the microsomal vesicle. The transfer of nascent protein across the microsomal membrane was not accompanied by any changes in phospholipid metabolism and occurred in the absence of adenosine triphosphate and of any added enzyme and also at 0°. The only requirement needed for transport of the nascent protein across the microsomal membrane is that it be released from the ribosomes.