Isotope exchange glutamine synthetase

The kinetic approach that has been most extensively applied to glutamine synthetase is that of equilibrium isotope exchange (85-88). Experimental procedures involve preparing a series of reaction solutions at chemical equilibrium and monitoring the following exchanges ... 

Recently Midelfort and Rose (4) introduced a positional isotope exchange technique that is also suitable for study by the chemical shift technique. Briefly, this technique follows the exchange of label from one part of a substrate to another due to rotational equivalence of some intermediate. The method was first applied to glutamine synthetase in the reaction ... 

To examine the kinetic competence of y-glutamyl phosphate formation at the active site of glutamine synthetase, the technique of positional isotope exchange (PIX) was introduced to studies of the mechanism of phospho transfer (85). This experiment circumvented the problem of the instability of the intermediate, which complicated direct kinetic experiments. In the PIX experiment, the rate at which glutamine synthetase catalyzes reaction (25) was measured. 

The positional isotopic exchange (PIX) technique involves observation of exchange of label between two positions in a reactant. The method was first used by Midelfort and Rose in 1976 to follow jS-y bridge to )8-nonbridge transfer of 0 in ATP incubated with glutamine synthetase (60) ... 

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