Exchange reactions glutamine synthetase

Electron paramagnetic resonance (continued) cobalt-thermolysin complex, 28 334, 335 exchange reactions, 31 106-107 glutamine synthetase, 28 358-364 invisible oxygen species, 31 94-95 metalloenzymes, 28 324, 326 metal particle size distribution, 36 99-100, 104... 

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 transferase reaction requires catalytic amounts of ADP and inorganic phosphate as well as a metal. In this reaction Mn++ is more effective than Mg++. Cysteine or another —SH compound activates the transferase as well as the synthetase reaction. L-Glutamine is much more effective in the exchange reaction than the D-isomer, and analogs of glutamine have low or no activity. 

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