An in vivo effect of the metabolites L-alanine and glycyl-L-leucine on the properties of lysyl-tRNA synthetase from Escherichia coli K-12. I. Influence on subunit composition and molecular weight distribution.

Lysyl-tRNA synthetase was purified to 70-90% of homogeneity from Escherichia coli K-12. The enzyme was purified from wild-type cells grown in minimal medium, or minimal medium containing either 20 mM L-alanine or 3 mM glycly-L-leucine. The synthetase was similarly purified from a mutant strain grown in minimal medium plus 20 mM L-alanine. Results based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration, and trypsin inactivation studies indicate (A) that the presence of L-alanine of glycyl-L-leucine in the culture medium alters the properties of the wild-type enzyme; (B) that the alteration of the synthetase by l-alanine and glycyl-L-leucine is different; and (c) that the molecular weight of lysyl-tRNA synthetase is at least 135000--140000. The results suggest that most likely the metabolites modify the structure of lysyl-tRNA synthetase, but the possibility that the metabolites induce the synthesis of a new lysyl-tRNA synthetase cannot be completely eliminated.