DDT increases the aminoacyl-tRNA binding activity of liver pH 5 supernatant fraction

The incorporation of [ 14C]phenylalanyl-tRNA into peptide was measured in cell-free preparations obtained from the liver of control rats and the liver of rats that had received DDT. Elongation factors 1 (EF 1) and 2 (EF 2), necessary for the binding of aminoacyl-tRNA to ribosomes and for the translocation of peptidyl-tRNA from the A site to the P site of ribosomes, were present in the pH 5 supernatant fractions of liver of control or DDT-treated rats and these fractions were incubated with saltwashed ribosomes obtained from the liver of control rats. The results provided evidence that the increased incorporation observed with the pH 5 supernatant fraction obtained from the DDT-treated rats could not be attributed to decreased ribonuclease activity or to increased EF 2 activity but was due to an increase in EF 1 activity. When EF 1 was separated from EF 2 by gel filtration chromatography, the activity of EF 1 from DDT-treated rats was greater than the activity of EF 1 from the control rats. Moreover, an increased binding of [ 14C]phenylalanyl-tRNA to ribosomes was found in the preparations obtained four the liver of DDT-treated rats, in further support of the conclusion that aminoacyl-tRNA binding is increased in rat liver after DDT treatment.