Sorbitol dehydrogenase of Aspergillus niger, SdhA, is part of the oxido-reductive D-galactose pathway and essential for D-sorbitol catabolism

In filamentous fungi D-galactose can be catabolised through the oxido-reductive and/or the Leloir pathway. In the oxido-reductive pathway D-galactose is converted to D-fructose in a series of steps where the last step is the oxidation of D-sorbitol by an NAD-dependent dehydrogenase. We identified a sorbitol dehydrogenase gene, sdhA (JGI53356), in Aspergillus niger encoding a medium chain dehydrogenase which is involved in D-galactose and D-sorbitol catabolism. The gene is upregulated in the presence of D-galactose, galactitol and D-sorbitol. An sdhA deletion strain showed reduced growth on galactitol and growth on D-sorbitol was completely abolished. The purified enzyme converted D-sorbitol to D-fructose with K-m of 50 +/- 5 mM and v(max) of 80 +/- 10 U/mg. (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.