Identification in the mould Hypocrea jecorina of a gene encoding an NADP(+): d-xylose dehydrogenase

A gene coding for an NADP(+)-dependent d-xylose dehydrogenase was identified in the mould Hypocrea jecorina (Trichoderma reesei). It was cloned from cDNA, the active enzyme was expressed in yeast and a histidine-tagged enzyme was purified and characterized. The enzyme had highest activity with d-xylose and significantly smaller activities with other aldose sugars. The enzyme is specific for NADP(+). The K(m) values for d-xylose and NADP(+) are 43 mM and 250 μM, respectively. The role of this enzyme in H. jecorina is unclear because in this organism d-xylose is predominantly catabolized through a path with xylitol and d-xylulose as intermediates and the mould is unable to grow on d-xylonic acid.