Compound as reactive (1)

NAD(P)H + 2-keto-L-gulonate + H⁺ → NAD(P)+ + L-idonate

Compound as product (3)

an oxidized electron donor + H₂O + L-sorbosone 2,6-lactone → a reduced electron donor + 2-keto-L-gulonate + H⁺

NAD(P)H + 2,5-didehydro-D-gluconate + H⁺ → NAD(P)+ + 2-keto-L-gulonate

2-keto-L-gulonate + NADP⁺ ← NADPH + 2,5-didehydro-D-gluconate + H⁺

Reversible reaction (2)

L-ascorbate + H₂O ↔ 2-keto-L-gulonate

L-idonate + NADP⁺ ↔ NADPH + 2-keto-L-gulonate + H⁺