Prokaryotic Bifunctional Glucose-6-phosphate Isomerase
In some archaea and bacteria glucose-6-phosphate isomerase (PGI) activity occurs via a bifunctional enzyme that also exhibits phosphomannose isomerase (PMI) activity. Though not closely related to eukaryotic PGIs, the bifunctional enzyme is similar enough that the sequence includes the cluster of threonines and serines that forms the sugar phosphate-binding site in conventional PGI. The enzyme is thought to use the same catalytic mechanisms for both glucose ring-opening and isomerisation for the interconversion of glucose 6-phosphate to fructose 6-phosphate.
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