An investigation was made of the thermal inactivation of lysyl-tRNA synthetase (L-lysine: tRNA ligase (AMP), EC 6.1.1.6) 400-fold purified from baker's yeast. During heat inactivation at pH 7.2, 45 degrees, the enzyme was stabilized by the presence of L-lysine or by ATP and MgCl2. The concentration of L-lysine giving half-maximal protection of the enzyme was decreased by the presence of ATP and MgCl2, or tRNA and MgCl2. Similarly, polyuridylate and polycytidylate enhanced the protection of the synthetase by L-lysine. No stabilization was given by any polynucleotide in the absence of L-lysine. Adenosine 5'-phosphate, adenosine 2'(3')-monophosphate, adenosine, 5-hydroxy-DL-lysine, and ethylene glycol each gave some stabilization of the enzyme in certain conditions. In a comparative study it was found that partially purified preparations of arginyl-tRNA synthetase (L-arginine: tRNA ligase (AMP), EC 6.1.1) from baker's yeast showed a different pattern of susceptibility to heat from that shown by the lysine enzyme. Low concentrations of L-arginine were less effective than tRNA and MgCl2 in stabilization of arginyl-tRNA synthetase from thermal inactivation at 50 degrees. The greatest protection was observed in the presence of L-arginine, tRNA, and MgCL2, whereas L-arginine, ATP, and MgCl2 gave lower protection. The characteristics of heat inactivation of the yeast aminoacyl-tRNA synthetases specific for lysine and arginine could be interpreted in terms of substrate-induced conformational changes in the enzyme proteins.

• PMID: 4315148
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Journal Article

Authors

Chlumecka V, Mitra SK, D'Obrenan P, Smith CJ

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