Construction of a bifunctional enzyme, lactate dehydrogenase/ galactose dehydrogenase, able to recycle NADH

Abstract

The in frame fusion between the galdh gene and the Idh gene encoding a linker region of five amino acids has been expressed in E.coli. The purified protein displays both enzyme activities and has a subunit molecular weight of 68500. The hybrid protein folds into a hexameric complex. When co-expressed with native galactose dehydrogenase both tetrameric and hexameric configurations are observed. In vitro observations show that the hybrid enzyme recycles NAD with a continuous production of îactate without any externally added NADH. A higher recycling rate compared to the rate of the native enzymes is observed at pH above 8.5. Proximity effects give the fusion enzyme advantages over the native enzymes and this phenomenon is especially pronounced when diffusion hindrance is applied during the recycling assay. This project was supported by the Swedish Research Council for Engineering Sciences (TFR).