MULTIPLE XYLITOL DEHYDROGENASE SYSTEM OF ASPERGILLUS ORYZAE

Abstract

Aspergillus oryzae P5 has some xylanolytic enzymes such as xylanase of 8.8 U/mg, α-L arabinofuranosidase of 1.2 U/mg, β- xylosidase of 1.9 U/mg and xylose reductase activities were 11.3 U/mg and 13.4 U/mg by using NADH and NADPH. However, xylitol dehydrogenase activities were 5.5 U/mg and 1.8 U/mg using NAD+ and NADP+ as cofactor, respectively. In genome of  A. oryzae, there are 4 fragments, which are homologous with  DNA xylitol dehydrogenase genes of other strains. Based on DNA  sequences of these fragments, 2 genes were cloned. One of them (xdhA) gene encodes for NAD+-dependent xylitol dehydrogenase activity. The gene was knock out in  A. oryzae  P5, however the mutant still showed NAD+

- dependent xylitol dehydrogenase activity. Therefore, A. oryzae  P5 has multiple xylitol dehydrogenases