Production of 4-deoxy-L-erythro-5-hexoseulose uronate from alginate by using endo- and exo-type alginate lyases

Alginate is the main carbohydrate component of brown algae that is considered as a promising source of third-generation biofuels and chemicals. Alginate can be enzymatically depolymerized to uronate monomers such as mannuronic acid and guluronic acid by alginate lyase. These monomeric sugar acids are further non-enzymatically converted to 4-deoxy-L-erythro-5-hexoseulose uronate (DEH). DEH can be fermented to biofuels or chemicals or it can be used as a platform chemical for bio-based products. In this study, an enzymatic saccharification process of using two recombinant alginate lyases, endo-type Alg7D and exo-type Alg17C, was developed for the efficient production of DEH from alginate. When sequential and simultaneous additions of Alg7D and Alg17C were compared, the final yield of DEH was significantly higher when the enzymes were added sequentially. The reaction progress of saccharification into DEH was verified by thin-layer chromatography and gas chromatography-mass spectrometry. These results suggest that the two recombinant enzymes can be further exploited for the production of DEH and third-generation biofuels from brown algal biomass.