Protein synthesis was significantly enhanced in subcellular systems containing ribosomes and cytosol from the liver of Walker
tumor-bearing rats from the second week following the
tumor transplantation and this enhancement persisted for the whole period of
tumor growth. Homologous systems from Zajdela
hepatoma and host liver showed a markedly increased
poly(U)-dependent
peptide elongation when compared with normal liver tissue. A stimulation of
polyphenylalanine synthesis resulted from the addition of cytosols from
tumors or host liver to ribosomes from normal rat liver. Similar results were found for the binding of phenylalanyl-
tRNA to ribosomes. Ribosomes from
tumors and host liver are more active in
peptide elongation than particles from normal liver tissue. A more than 10-fold stimulation of
phenylalanine polymerization resulted from the addition of
poly(U) to ribosomes from Zajdela
hepatoma whereas only less than 2-fold enhancement was found when using ribosomes from normal or host liver.
Hepatoma ribosomes apparently contain only a low proportion of polyribosomes carrying natural message. Enhanced
protein synthesis in
tumors and host liver is apparently due, in particular, to an increased activity of soluble factors required for
protein synthesis and less due to an increased activity of ribosomes.