Studies on Seryl and Phenyl-alanyl Synthetases from Ascitic Tumor Cells Treated with 20-Methylcholanthrene

Abstract

Summary

The aminoacylation of tRNA is an important step in the regulation of protein synthesis. The aminoacyl-tRNA synthetases may have a regulatory function in the transformation of normal cells to neoplastic cells.

Seryl and phenylalanyl synthetase have been isolated from ascitic tumor cells which were previously treated with 20-methyl-cholanthrene. The different steps of preparation are (NH₄)₂SO₄ precipitation of the 105,000g supernatant (between 50 and 65% saturation), chromatography on DEAE cellulose, CM Sephadex C-50 and hydroxy-apatite.

The purification fold of the seryl-tRNA synthetase was 450 times with the molecular weight of 120,000. The present studies have shown that the K _m for serine was about 20 times higher in MCA-treated cells than in the controls, while the K _m for ATP was only increased 3–4 times. These values indicate that the synthetases possibly have a regulatory role in the protein synthesis of the cancer cells with and without treatment with MCA. Similar differences were not found in the case of phenylalanyl synthetase.