4-Deoxy-l-erythro-5-hexoseulose Uronate (DEH) and DEH Reductase: Key Molecule and Enzyme for the Metabolism and Utilization of Alginate

4-Deoxy-l-erythro-5-hexoseulose uronate (DEH), DEH reductase, and alginate lyase have key roles in the metabolism of alginate, a promising carbon source in brown macroalgae for biorefinery. In contrast to the widely reviewed alginate lyase, DEH and DEH reductase have not been previously reviewed. Here, we summarize the current understanding of DEH and DEH reductase, with emphasis on (i) the non-enzymatic and enzymatic formation and structure of DEH and its reactivity to specific amino groups, (ii) the molecular identification, classification, function, and structure, as well as the structural determinants for coenzyme specificity of DEH reductase, and (iii) the significance of DEH for biorefinery. Improved understanding of this and related fields should lead to the practical utilization of alginate for biorefinery.