Abstract

Xuejiao Chen, Haitao Ding, Yiqing Du, Hui Lin, Zeli Li and Yuhua Zhao*

The glucose dehydrogenase gene (gdh), cloned from Bacillus sp. G3, was composed of 786 bp nucleotide and the deduced protein molecular mass of one subunit was 28.1 kDa. The recombinant glucose dehydrogenase (rGDH-G3) was functionally expressed in Escherichia coli. The results revealed that expressed rGDH-G3 had a high specific activity of 371.9 U/mg at 25°C and pH 8.0, with oxidized nicotinamide adenine dinucleotide (NAD+ ) as the cofactor. The enzyme was optimally active at 40°C and pH 9.0. The enzyme displayed broad specificity for other sugars such as D-galactose or maltose. The catalytic efficiency of the rGDH-G3 would be improved 4 times when oxidized nicotinamide adenine dinucleotide phosphate (NADP+ ) was used as cofactor instead of NAD+ .