Characterization of uronate dehydrogenases catalysing the initial step in an oxidative pathway

Summary Uronate dehydrogenases catalyse the oxidation of uronic acids to aldaric acids, which represent ‘top value‐added chemicals’ that have the potential to substitute petroleum‐derived chemicals. The identification and annotation of three uronate dehydrogenases derived from F ulvimarina pelagi   HTCC 2506, Streptomyces viridochromogenes   DSM 40736 and O ceanicola granulosus   DSM 15982 via sequence analysis is described. Characterization and comparison with two known uronate dehydrogenases in regard to substrate spectrum, catalytic activity and pH as well as temperature dependence was performed. The catalytic efficiency was investigated in two different buffer systems; potassium phosphate and T ris‐ HCl . In addition to the typical and well available substrates glucuronate and galacturonate also mannuronate as part of many structural polysaccharides were tested. The uronate dehydrogenase of Agrobacterium tumefaciens and P seudomonas syringae showed catalytic dependency on the buffer system resulting in an increased K m especially for glucuronate in potassium phosphate compared with T ris‐ HCl buffer. Enzyme stability at 37°C of the different U dhs was in the order: P . syringae  <  S . viridochromogens  <  A . tumefaciens  <  F . pelagi  <  O .  granulosus . All enzymes showed activity within a broad pH range from 7.0 to 9.5, only O . granulosus had a very narrow range around 7.0.