The 1-deoxyxylulose 5-phosphate reductoisomerase (DXR, )catalyzes the conversionof 1-deoxy-D-xylulose 5-phosphate (DXP)into 2-C-methyl-D-erythritol 4-phos-phate (MEP). This transformation is a two-step process involving a rearrangement of DXP into the putative inter-mediate 2-C-methyl-D-erythrose 4-phosphate followed by a NADPH-dependent reduction of the latter aldehyde. By using [1-13 C]DXP as a substrate, the rearrangement of DXP into [5-13 C]2-C-methyl-D-erythrose 4-phosphate was shown to be NADPH dependent, although it does not involve a reduction step. .
