[Role of arginine residues in phenylalanyl-tRNA synthetase interaction with substrates].

The effect of 2,4-pentandione on the activity of phenylalanyl-tRNA synthetase (Phe-RSase) from E. coli MRE-600 was investigated. Modification of arginine residues of Phe-RSase with 2,4-pentandione was shown to decrease the rate of both ATP-[32P]pyrophosphate exchange and aminoacylation reaction. In the presence of Mg2+ ions ATP essentially protects the enzyme from inactivation. L-Phe has practically no protective effect. There are no changes in the values of Km for tRNAPhe in the aminoacylation reaction and for amino acid in ATP-[32P]pyrophosphate exchange and aminoacylation reaction while Km for ATP is increased in both. Modification of 42-44 arginine residues per molecule of the enzyme causes loss of 50% of the enzyme activity for tRNA aminoacylation. Under these conditions ATP in the presence of Mg2+ ions as well as ATP + Mg2+ combined with L-Phe, protects 8-10 arginine residues per molecule of the enzyme from modification. Part of arginine residues of the enzyme molecule is assumed to be essential for ATP binding.