The present invention relates to isolated nucleic acid molecules encoding mutants of glucose-6-phosphate dehydrogenase, and vectors and hosts cells including such nucleic acid molecules. These nucleic acid molecules are involved in the biosynthesis of a fine chemical, e.g., an amino acid such as lysine. The present invention also relates to methods of producing and modulating the production of fine chemicals, e.g., lysine, by culturing recombinant microorganisms containing these nucleic acid molecules under conditions such that the fine chemical is produced.