Phosphoryl group, transfer phosphoglucomutases

Mutase Transfer of phosphoryl group between sites on substrate Phosphoglucomutase (glucose-6-phosphate glucose-1-phosphate) ... 

Figure 21.5. Reaction Catalyzed by Phosphoglucomutase. A phosphoryl group is transferred from the enzyme to the substrate, and a different phosphoryl group is transferred hack to restore the enzyme to its initial state.

Phosphoglucomutase catalyzes the reversible transfer of a phosphoryl group from the 1 or 6 position of glucose 1,6 diphosphate to a serine hydroxyl group on the enzyme yielding a phosphoenzyme intermediate... 

Since metal coordination or immobilization of the transferred phosphoryl group by multiple hydrogen bonds would inhibit the formation of a metaphosphate intermediate in an S l mechanism and would facilitate nucleophilic attack in an Sy2 mechanism, the latter process seems likely for the reactions catalyzed by staphylococcal nuclease, DNA polymerase, pyruvate kinase, fructose diphosphatase, phosphoglucomutase, (Na + K) ATPase and possibly PEP carboxylase. In creatine kinase where an S l mechanism is possible, the enzyme would have to prevent access of nucleophiles other than ADP and creatine to the reactive metaphosphate intermediate. 

Some of the uncertainty about the transition state of the reaction of some enzymes, like p-phosphoglucomutase-catalyzed transfer of a phosphoryl group to a substrate in sugar metabolism, was resolved recently. Allan and Dunaway demonstrated that by means of nuclear magnetic resonance that the transition state involved a bipyramidal oxyphosphorane intermediate [72]. 

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