Arginyl-tRNA Synthetase from Escherichia coli. Influence of Arginine Biosynthetic Precursors on the Charging of Arginine-Acceptor tRNA with [14C]Arginine

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Abstract
The behavior of arginyl-tRNA synthetase (EC 6.1.1.19) in the presence of the arginine biosynthetic precursors, argininosuccinate, ornithine and citrulline, was studied in several E. coli K12 strains and in E. coli W. The results of kinetic measurements with partially purified extracts indicate that the arginyl-tRNA synthetase of E. coli is not inhibited by the arginine precursors. The apparent Km for arginine of the K12 enzyme is about 3.4 .mu.M in the absence and in the presence of these precursors, whereas the W enzyme exhibited an apparently slightly lowered Km and a decreased [14C]arginyl-tRNA equilibrium level in the presence of argininosuccinate. This was due to isotopic dilution of [14C]arginine by non-radioactive amino acid formed from argininosuccinate by argininosuccinate lyase (EC 4.3.2.1) contaminating the synthetase preparation. This finding emphasizes the necessity of using pure arginyl-tRNA synthetase in order to study the possible regulatory involvement of this enzyme in the control of the arginine regulon in vitro.