Figure 19-23

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Ribbon drawing of ferredoxin–NADP+ reductase (FNR) from peas. Residues 514 to 648 (gold) fold into an antiparallel beta barrel, which contains the FAD binding site. Residues 649 to 808 (purple), which provide the bulk of the NADP+ binding site, form a Rossmann fold. FAD and NADP+ are shown in stick form with FAD C cyan, NADP+ C green, N, O, and P atoms blue, red, and yellow, respectively. The flavin and nicotinamide rings are in opposition with C4 of the nicotinamide ring and C5 of the flavin ring 3.0 Angstroms apart, an arrangement that is consistent with direct hydride transfer as also occurs in dihydrolipoyl dehydrogenase (Figure 17-8). However, in contrast to this latter enzyme, whose bound flavin and nicotinamide rings are parallel, those in FNR are inclined by ~30°, a heretofore unobserved binding mode. [Based on an X-ray structure by Andrew Karplus, Cornell University. PDBid 1QFY.]