Crystallization and properties of 5-keto-d-gluconate reductase from Gluconobacter suboxydans.

5-Keto-n-gluconate reductase (EC 1.1.1.69) was purified and crystallized for the first time from cell-free extract of Gluconobacter suboxydans IFO 12528. Purification of the enzyme was successfully performed by column chromatography on DEAE-Sephadex A-50, bluedextran Sepharose 4B, followed by pH gradient chromatography on DEAE-Sephadex A-50. The enzyme was purified about 1200-fold with an overall yield of 40%. The enzyme was much stabilized against heating and storage by adding either D-gluconate or 5-keto-n-gluconate. 2-Keto-D-gluconate had no effect to stabilize the enzyme and the enzyme was confirmed to be a different entity from 2-keto-D-gluconate reductase stabilized by gluconate or 2-keto-n-gluconate but not 5-keto-D-gluconate. It was also confirmed with crystalline enzyme that 5-keto-D-gluconate reductase is considered to have a function to reduce intracellular 5-keto-D-gluconate to D-gluconate in combination with regeneration of NADP.