XYLOSE METABOLISM IN A THERMOPHILIC MOLD MALBRANCHEA-PULCHELLA VAR SULFUREA TMD-8

The thermophilic mould Malbranchea pulchella var. sulfurea TMD-8 produced extracellular xylanases in wheat straw hemicellulose as well as wheat straw. This mould utilized xylose less efficiently than glucose. Mycelial extracts contained xylose isomerase, xylose reductase, and xylitol dehydrogenase. Xylose isomerase was less thermostable than that from other microorganisms. However, xylitol dehydrogenase and xylose reductase were relatively more thermostable in comparison with these enzymes from other microorganisms. The affinity of xylose isomerase for xylose was very high (Km 10 mM), while that of xylose reductase was low (Km 23.5 mM). The xylitol dehydrogenase exhibited relatively high affinity for xylitol (Km 0.02 mM). The activity of this enzyme, however, declined steeply, in the alkaline range. This is the first report on the occurrence of three intracellular enzymes, xylose isomerase, xylose reductase, and xylitol dehydrogenase in a thermophilic mould, which play an important role in xylose metabolism.