Glucose 1,6-bisphosphate synthase using 1,3-bisphosphoglycerate as a phosphate donor and a series of 1-phosphate sugars, including glucose 1-phosphate, mannose 1-phosphate, ribose 1-phosphate and deoxyribose 1-phosphate, as acceptors (PubMed:17804405). In vitro, also exhibits very low phosphopentomutase and phosphoglucomutase activity which are most probably not physiologically relevant (PubMed:17804405).