1-deoxy-D-xylulose 5-phosphate reductoisomerases catalyze the formation of 2-C-methyl-D-erythritol 4-phosphate from 1-deoxy-D-xylulose-5-phosphate (DXP) in the presence of NADPH. This reaction is the second step of the deoxyxylulose 5-phosphate/methylerythritol 4-phosphate pathway (the terpenoid biosynthesis pathway) found in many bacteria and plants. The end product, isopentenyl diphosphate, is the precursor of various isoprenoids vital to all living organisms. This pathway is not found in humans, where the mevalonate pathway is used for the formation of isopentenyl diphosphate instead. This aspect makes the reductoisomerase an excellent drug target in a number of pathogenic organisms. The family of 1-deoxy-D-xylulose 5-phosphate reductoisomerases is a member of the FAD/NAD(P)-binding Rossmann fold Superfamily. The superfamily contains redox enzymes consisting of two domains. One domain determines substrate specificity and the reaction of the enzyme. The other domain, which is common to this superfamily, is a Rossmann-fold domain and binds nicotinamide adenine dinucleotide (NAD+).