Catalyzes the conversion of the nucleoside breakdown products ribose-1-phosphate and deoxyribose-1-phosphate to the corresponding 5-phosphopentoses (PubMed:17804405). Catalyzes the reversible isomerization of alpha-D-glucose 1-phosphate to alpha-D-glucose 6-phosphate but with a lower catalytic efficiency (PubMed:17804405). The mechanism proceeds via the intermediate compound alpha-D-glucose 1,6-bisphosphate (PubMed:17804405). In vitro, has also a low glucose 1,6-bisphosphate synthase activity which is most probably not physiologically relevant (PubMed:17804405, PubMed:18927083).
