Methionyl-tRNA synthetase from Escherichia coli. Absence of interaction between the metal ion and the purine ring of ATP in the L-methionine activation site.

Enhancement of the nuclear relaxation rates by manganese has been used to derive manganese--purine-ring distances in the activation site of methionyl-tRNA synthetase. This is possible with the help of an abortive complex between the enzyme, methionine, adenosine, pyrophosphate and manganese which simulates an intermediate species of the activation reaction. It is found that the distances between the manganese ion and the purine ring are too high (greater than 0.8 nm) to allow interaction between them. Thus, metal-purine interaction is involved neither in the catalytic mechanism nor in the stabilization of abortive synergistic complexes [S. Blanquet, G. Fayat and J. P. Waller (1975) J. Mol. Biol. 94, 1-15].