The structures of NADP+ and magnesium isocitrate bound to the NADP(+)-dependent isocitrate dehydrogenase of Escherichia coli have been determined and refined at 2.5-A resolution. NADP+ is bound by the large domain of isocitrate dehydrogenase, a structure that has little similarity to the supersecondary structure of the nucleotide-binding domain of the lactate dehydrogenase-like family of nucleo...