Modification of the in vitro Amino Acid Incorporation Capacity of Rat Liver after in vivo and in vitro Treatments

Rats were maintained for several days on a protein‐free carbohydrate containing diet which was changed to a protein‐rich diet approximately 14–17 h before decapitation. The ability to incorporate amino acids into protein was enhanced after the nutritional alteration, and this enhancement was unaffected by pretreatment in vivo with the antibiotics actinomycin d and chloramphenicol. Molecular sieving of microsomes and cell sap through Sephadex G‐25 removed components or factors from the fractions. Under these conditions and in the presence of optimal amounts of cell sap, GTP and an amino acid mixture stimulated the incorporating activity of the preparations in a manner such that the originally observed differences between the two types of rats became less. These results were interpreted to suggest that the in vivo predetermined capacity of protein synthesis could be altered. These alterations implied an increase rather than a decrease of the originally in vitro observed amino acid incorporating activities.