Catalyzes the isomerization of sulfoquinovose (SQ) to 6-deoxy-6-sulfo-D-fructose (SF) (By similarity). In vitro, can also catalyze the interconversion of mannose, fructose and glucose, but has extremely low activity with glucose (PubMed:18328504). 6-sulfo-beta-D-quinovose = 6-deoxy-6-sulfo-D-fructose kcat is 23.3 sec(-1) for D-mannose. kcat is 12.3 sec(-1) for D-fructose. Homohexamer. Belongs to the N-acylglucosamine 2-epimerase family.