Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 7, 1997
Publication Date: N/A
Technical Abstract: Most yeasts metabolize xylose by first reducing xylose to xylitol, with xylose reductase and NADPH, and then oxidizing xylitol to xylulose, with xylitol dehydrogenase and NAD**+. Thereafter, xylulose is phosphorylated to xylulose-5-phosphate and metabolized via the pentose-phosphate pathway. The yeast genes for the initial steps in the xylose pathway have been cloned and successfully expressed in yeast that were unable to utilize xylose. The results indicated that a cofactor imbalance between NAD**+ and NADPH resulted in the incomplete conversion of xylose to xylulose. Hofer et al. (1971. Biochem. Biophys. Acta 252:1-12) examined the pathway of xylose metabolism in the yeast Rhodosporidium toruloides, syn. Rhodotorula glutinis. They presented strong circumstantial evidence that the primary route of xylose catabolism in this yeast was the direct conversion of xylose to xylulose by xylose isomerase. We examined the pathway that this yeast uses to metabolize xylose to determine if it does indeed possess a xylose isomerase. We were unable to detect xylose isomerase activity in cell free extracts; however, xylose reductase and xylitol dehydrogenase activities were readily detectable. If R. toruloides does possess a xylose isomerase, it does not play a major role in the catabolism of xylose.