Studies on two groups of aminoacyl-tRNA synthetases from rat liver.

Aminoacyl-tRNA synthetases from rat-liver cytoplasm were fractionated into two groups, characterized by their sedimentation coefficients of about 20S and 5S, respectively. These two groups of synthetases could be isolated from postmicrosomal supernatant either by gradient centrifugation, by gel filtration or by acid treatment at pH 5.2. Both groups were required for maximal amino acid incorporation in a cell-free system.