Isolation and Characterization of Two Methionine: tRNA Ligases from Wheat Germ

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Abstract
Two methionine:tRNA ligases (ligases A and B) with distinctly different enzymatic and molecular properties were isolated in homogeneous form from extracts of raw wheat germ. Both the A and B enzyme are composed of single polypeptide chains of MW 105,000 and 70,000, respectively. The smaller molecule (B) was probably not a proteolytic fragment of the larger one (A). The catalytic properties of both the A and B enzymes were established and the Mg2+-dependent capacity to charge 6 purified methionine-accepting tRNA were compared with those of the methionine:tRNA ligases from Escherichia coli and bakers'' yeast. The possible reasons for the presence of 2 methionine:tRNA ligases and their unusual monomeric nature are discussed.