Ligases

Methionyl-tRNA synthetase from Escherichia coli catalyses the activation of ['802]methionine by adenosine 5'-[(R)-cc''O]triphosphatewith inversion of configuration at P". Furthermore methionyl-tRNA synthetase does not catalyse positional isotope exchange in adenosine 5'-[j+ '80,]triphosphate in the absence of methionine or in the presence of the competitive inhibitor, methioninol, which eliminates the possibility of either adenylyl-enzyme or adenosine metaphosphate intermediates being involved. These observations require that methionyl-tRNA synthetase catalyses the activation of methionine by an associative 'in-line' nucleotidyl transfer mechanism.A kinetic study of positional isotope exchange in adenosine 5'- [~-180,]triphosphate in the presence of methionine, M$+ and methionyl-tRNA synthetase showed that torsional equilibration ( l 8 0 exchange into the P"-0-PP bridge) occurs faster than tumbling (l80 exchange into Py by rotation about the C, axis of Mg ['80,]

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An investigation of the mechanism of activation of tryptophan by tryptophanyl‐tRNA synthetase from beef pancreas

Lowe

Tansley

1984

European Journal of Biochemistry

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Adenosine (S)‐5′‐[α‐17O,18O2]triphosphate has been synthesized and used to investigate the stereochemical course of activation of tryptophan by tryptophanyl‐tRNA synthetase from beef pancreas. It is shown that the reaction proceeds by displacement of Mg pyrophosphate from MgATP with inversion of configuration at Pot. Tryptophanyl‐tRNA synthetase catalyses positional isotope exchange in adenosine 5′‐[β‐18O2]triphosphate in the presence of tryptophan but not in its absence or in the presence of the competitive inhibitors tryptamine and tryptophanol. These observations eliminate a multi‐adenylyl transfer or dissociative mechanism and in combination with the stereochemical study leave a direct associative ‘in line’ displacement at Pα of MgATP as the only tenable mechanism for the activation of tryptophan by tryptophanyl‐tRNA synthetase.

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Ligases

Cited by 3 publications

References 89 publications

Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap₄A

Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap₄A

A Stereochemical and Positional Isotope‐Exchange Study of the Mechanism of Activation of Methionine by Methionyl‐tRNA Synthetase from Escherichia coli

An investigation of the mechanism of activation of tryptophan by tryptophanyl‐tRNA synthetase from beef pancreas

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Ligases

Cited by 3 publications

References 89 publications

Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap4A

Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap4A

A Stereochemical and Positional Isotope‐Exchange Study of the Mechanism of Activation of Methionine by Methionyl‐tRNA Synthetase from Escherichia coli

An investigation of the mechanism of activation of tryptophan by tryptophanyl‐tRNA synthetase from beef pancreas

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Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap₄A

Stereochemical Analysis of the Enzymic Synthesis and Hydrolysis of Ap₄A