Mechanisms of biological phosphate transfer to and from carbohydrates

Although the possibility of pseudorotation during enzymic phosphoryl transfer has been raised many times, there is as yet no unambiguous example of it. If groups enter and leave from apical positions, the trigonal bipyramidal intermediate may have a lifetime less than the period of a vibration and thus be too unstable to exist. In practice, therefore, the rule retention = double displacement, inversion = single displacement appears to hold for phosphoryl transfer at least as well as for glycosyl transfer. 

Mg and soft metals such as being used. The ability to replace a phosphate oxygen by sulfur, in combination with the use of soft metals by phosphoryl-transferring enzymes, provides an important probe of stereochemistry and mechanism. If sulfur is incorporated at a site coordinating to (or a hydrogen bond donor such as lysine), catalysis is gravely impaired, whereas if the coordination is to Zn there is little effect. 

In general, kinases act with inversion and mutases act with retention, whereas phosphatases act with either with inversion or retention. 

Fructose 1,6-diphosphatase hydrolyses off the 1-phosphate in the step which commits the substrate to gluconeogenesis. The mammalian enzyme, a homodimer, is richly allosteric, as befits an enzyme at a metabolic branchpoint. It catalyses a single displacement, mediated by no less than four metal ions three Mg sites and one K site have been observed in the crystal structure. The nucleophilic water may be activated by proton transfer from Glu98. The very large claim has been made that by alteration of the conditions of crystallisation, the on-enzyme equilibrium can be switched from fructose-6-phosphate and inorganic phosphate to fructose-6-phosphate and metaphosphate. Given the 

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