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. In vitro, also exhibits very low phosphopentomutase and phosphoglucomutase activity which are most probably not physiologically relevant. (2R)-3-phospho-glyceroyl phosphate + alpha-D-glucose 1-phosphate = (2R)-3-phosphoglycerate + alpha-D-glucose 1,6-bisphosphate + H(+) (2R)-3-phospho-glyceroyl phosphate + alpha-D-glucose 6-phosphate = (2R)-3-phosphoglycerate + alpha-D-glucose 1,6-bisphosphate + H(+) (2R)-3-phospho-glyceroyl phosphate + alpha-D-ribose 1-phosphate = (2R)-3-phosphoglycerate + alpha-D-ribose 1,5-bisphosphate + H(+) (2R)-3-phospho-glyceroyl phosphate + 2-deoxy-alpha-D-ribose 1-phosphate = (2R)-3-phosphoglycerate + 2-deoxy-alpha-D-ribose 1,5-bisphosphate + H(+) (2R)-3-phospho-glyceroyl phosphate + alpha-D-mannose 1-phosphate = (2R)-3-phosphoglycerate + alpha-D-mannose 1,6-bisphosphate + H(+) Expressed at highest levels in the brain and testis, at intermediate levels in thymus, spleen, lung and skeletal muscle, and at lowest levels in kidney, liver and heart. Belongs to the phosphohexose mutase family.