Induction of NADPH-linked D-xylose reductase and NAD-linked xylitol dehydrogenase activities in Pachysolen tannophilus by D-xylose, L-arabinose, or D-galactose
✍ Scribed by P. L. Bolen; R. W. Detroy
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 626 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0006-3592
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✦ Synopsis
Considerable interest in the D-xylose catabolic pathway of Pachysolen tannophilus has arisen from the discovery thatthis yeast iscapableoffermenting D-xylosetoethanol. In this organism D-xylose appears to be catabolized through xylitol to D-xylulose. NADPH-linked D-xylose reductase is primarily responsible for the conversion of D- xylose to xylitol, while NAD-linked xylitol dehydrogenase is primarily responsible for the subsequent conversion of xylitol to o-xylulose. Both enzyme activities are readily detectable in cell-free extracts of P. tannophilus grown in medium containing D-xylose, L-arabinose, or D-galactose and appear to be inducible since extracts prepared from cells grown in media containing other carbon sources have only negligible activities, if any. Like D-xylose, Larabinose and D-galactose were found t o serve as substrates for NADPH-linked reactions in extracts of cells grown in medium containing D-xylose, L-arabinose, or o-galactose. These L-arabinose and D-galactose NADPHlinked activities also appear to be inducible, since only minor activity with L-arabinose and no activity with Dgalactose is detected in extracts of cells grown in Dglucose medium. The NADPH-linked activities obtained with these three sugars may result from the actions of distinctly different enzymes or from a single aldose reductase acting on different substrates. High-performance liquid chromatography and gas-liquid chromatography of in vitro D-xylose, L-arabinose, and D-galactose NADPHlinked reactions confirmed xylitol, L-arabitol, and galactitol as the respective conversion products of these sugars. Unlike xylitol, however, neither L-arabitol nor galactitol would support comparable NAD-linked reaction(s) in cellfree extracts of induced P. tannophilus. Thus, the metabolic pathway of D-xylose diverges from those of L-arabinose or D-galactose following formation of the pentitol. * The mention of firm names or trade products does not imply that they are endorsed or recommended by the US. Department of Agriculture over other firms or similar products not mentioned.