Wulf Crueger

Glucose Transforming Enzymes

The metabolism of glucose is an important part of the primary metabolism in microorganisms. Therefore, the attack of microorganisms on glucose results in a broad range of reactions. A complete utilization may be observed, resulting in the production of CO2, H2O, and cell mass. In other cases only slight alterations of the molecule may occur. These latter reactions, such as incomplete oxidations, aldose-ketose isomerization or glycosyl-transfer may also be used for commercial glucose conversion. This review is chiefly concerned with some of these reactions and will not deal with the many intermediary steps of primary metabolism. The most important glucose transforming enzyme from a commercial viewpoint is glucose isomerase. Other well-known enzymes are the glucose oxidases; the preferred position for the oxidation of glucose is C-1, yielding gluconic acid. Further oxidations of gluconic acid yield after several steps 2-keto-l-gulonic acid (KGA). KGA is an intermediate in commercial production of ascorbic acid, where either a combination of microbial conversion steps via 2-ketogluconic acid and 2,5-diketo-d-gluconic acid results in KGA, or where gluconic acid is oxidized enzymatically to 5-keto-d-gluconate, which after catalytic hydrogenation to calcium l-gulonate, is transformed to KGA by several microorganisms. These pathways are reviewed by Crueger & Crueger (1984).