Oxidizes both D-glucose and D-mannose, but is 15 times more catalytically efficient with mannose. Strictly dependent on NADP. D-glucose + NADP(+) = D-glucono-1,5-lactone + H(+) + NADPH kcat is 84.8 sec(-1) with glucose as substrate. kcat is 106 sec(-1) with mannose as substrate. Homotetramer or homooctamer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.