This enzyme, formally named (1->4)-alpha-D-glucan 1-alpha-D-glucosylmutase, is the TreY enzyme of the TreYZ pathway of trehalose biosynthesis, an alternative to the OtsAB pathway. Trehalose may be incorporated into more complex compounds but is best known as compatible solute. It is one of the most effective osmoprotectants, and unlike the various betaines does not require nitrogen for its synthesis. [Energy metabolism, Biosynthesis and degradation of polysaccharides]