Disclosed is a method for the isomerization of glucose by reduction to sorbitol and subsequent oxidation to fructose, in which the redox cofactors NAD+/NADH and NADP+/NADPH are regenerated in a one-pot-reaction, wherein one of the two redox cofactors is obtained in the reduced form thereof and the other redox cofactor in the oxidized form thereof as a result of at least two additional enzymatically catalyzed redox reactions (product forming reactions) taking place in the same reaction batch, wherein a) in the regeneration reaction, which transfers the reduced cofactor back to its originally oxidized form, oxygen or a compound of the general formula R1C(O)COOH is reduced, and b) in the regeneration reaction, which transfers the oxidized cofactor back to its originally reduced form, a compound of the general formula R2CH(OH)R3 is oxidized, wherein R1, R2 and R3 have different meanings in the compounds, characterized in that a mixture of glucose and fructose is used as a starting material. Furthermore, the use of fructose thus produced in a method for producing furan derivatives is disclosed.