NONPHOSPHOROLYTIC PATHWAY FOR D-GALACTONATE CATABOLISM IN ASPERGILLUS-TERREUS

The abilities of six species of fungi to utilize and degrade D-galactose as the sole carbon source were compared. A nonphosphorolytic pathway for D-galactonate catabolism was found to be operative by a cell-free extract of D-galactonate-grown mycelia of Aspergillus terreus. This extract has the capability (in the absence of ATP) to degrade D-galactonate into 2-keto-3-deoxy-D-galactonate (KDGal) by a D-galactonate dehydratase. KDGal was then degraded by a KDGal aldolase to produce pyruvate and glyceraldehyde. The same extract also activates the reverse reaction of aldolase. KDGal and pyruvate were identified chromatographically as the products of such a pathway. Results show the importance of Mg2+ for D-galactonate dehydratase activity. This pathway can be summarized as follows: D-Galactonate D-galactonate --> dehydratase 2-keto-3-deoxy-D-galactonate (KDGal) [GRAPHICS] Pyruvate + glyceraldehyde