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

The thermophilic mould Malbranchea pulchella var. sulfurea TMD-8 produ ced extracellular xylanases in wheat straw hemicellulose as well as wh eat straw. This mould utilized xylose less efficiently than glucose. M ycelial extracts contained xylose isomerase, xylose reductase, and xyl itol dehydrogenase. Xylose isomerase was less thermostable than that f rom other microorganisms. However, xylitol dehydrogenase and xylose re ductase were relatively more thermostable in comparison with these enz ymes from other microorganisms. The affinity of xylose isomerase for x ylose was very high (Km 10 mM), while that of xylose reductase was low (Km 23.5 mM). The xylitol dehydrogenase exhibited relatively high aff inity for xylitol (Km 0.02 mM). The activity of this enzyme, however, declined steeply, in the alkaline range. This is the first report on t he occurrence of three intracellular enzymes, xylose isomerase, xylose reductase, and xylitol dehydrogenase in a thermophilic mould, which p lay an important role in xylose metabolism.