earticle

영어

Xylose reductase (XR) is a key enzyme in D-xylose metabolism, catalyzing the reduction of D-xylose to xylitol. Expression of XR in Candida tropicalis is significantly repressed in cells grown on glucose by catabolic repression. This is one of the reasons that glucose cannot be used as a cosubstrate in xylitol production. A gene encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was isolated from the genomic DNA of C. tropicalis ATCC 20913 to construct a constitutive expression cassette for this strain. The endogenous XR gene (xyl1) was placed under the control of GAPDH promoter and integrated into the genome of C. tropicalis N43 which is xyl2-disrupted and xyl1-partially disrupted mutant. Expression of XR was confirmed by determining enzyme activity in cells grown on a medium containing glucose as a carbon source. The resulting recombinant yeast, C. tropicalis JA4, showed higher XR activity (550mU/mg of proteins) than that of the parental strain (18mU/mg of proteins). Batch culture was performed for xylitol production with JA4 using glucose as a cosubstrate. The initial xylitol production rate of JA4 was higher than that of the parental strain.