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Further Studies on Tumor and Liver Amino Acid Incorporating Systems

( Department of Biochemistry, The University of Texas, M. D. Anderson Hospital and Tumor Institute, Houston, Texas)

Amino acid activating and ribosomal fractions were prepared from normal rat liver, Novikoff ascites tumor cells, and Escherichia coli. Protein or peptide biosynthesis was studied under a range of conditions, and also by substitution of the fractions obtained from the different cells or tissues. The E. coli system was the most active in amino acid incorporation, tumor was intermediate, and the liver system least active. Activating and ribosomal fractions from liver and tumor were interchangeable. However, little or no incorporation was observed when the mammalian fractions were substituted for those from E. coli.

The requirement for guanosine triphosphate (GTP) in mammalian amino acid incorporating systems varied considerably. However, amino acid activating and ribosomal fractions that had a high exogenous GTP requirement were isolated from liver and tumor. GTP did not enhance amino acid incorporation in in vitro systems that were inhibited by puromycin. A large proportion of the peptide synthesized by the mammalian systems was held by the ribosomes and not released to the surrounding medium. GTP resulted in a severalfold increase in the quantity of C¹⁴-lysine in the ribosomal fraction but had little effect upon the release of the labeled peptides.

Additional studies were carried out to determine if exogenous ribonucleic acid (RNA) would enhance amino acid incorporation by the mammalian systems. RNA from tobacco mosaic virus (TMV) did result in a 40–100% increase for the amino acids tested. The tumor system responded to some synthetic polynucleotides in the same manner as that reported for E. coli and some mammalian systems.

Received 9/30/64.