Heavy and light forms of some aminoacyl-tRNA synthetases in fraction X,microsomes and cytosol of rabbit liver

Summary Aminoacyl-tRNA synthetase activity for alanine, glutamic acid, lysine and phenylalanine was studied in the three subcellular fractions of rabbit liver: fraction X, microsomes and cytosol. From 60 to 80% of the enzyme activities were found in fraction X and microsomes. Fraction X was especially rich in the synthetase activities. By means of gel chromatography, heavy (over 10⁶ daltons) and light (below 480 × 10³ daltons) forms of lysyl- and phenylalanyl- but only light ones of alanyl- and glutamyl-tRNA synthetase activities were found in all the subcellular fractions studied. It is concluded that in higher organisms (mammals) all aminoacyl-tRNA synthetases, at least in part, are associated with cell structural constituents.Abbreviations ALA, GLU, LYS, PHE alanyl-, glutamyl-, lysyl-, phenylalanyl-tRNA synthetase - PMSF phenylmethylsulfonyl fluoride - BSA bovine serum albumin