Abstract: The present invention describes the genetic engineering of production microorganisms used in biotechnology to improve their properties so that they produce industrially useful products more efficiently from fermentable sugars derived from biomass. The engineered microorganisms endowed with functional coupling of oxidation and reduction of substrates by dehydrogenases requiring pyridine nucleotides (NAD/NADH) result in simultaneous enhancement of reduction potential enzyme activity involving the transfer of electrons. In particular, this invention relates to the construction of an excisable gene expression cassette for expression of two different dehydrogenases leading to enhanced production of ethanol.