Structure of a human glutathione reductase dimer. The protein backbones of the 2 subunits are shown as ribbons. f1 indicates FAD domain 1; f2, FAD domain 2; and n, NADPH domain. The enzyme's FADs are shown in yellow. Each monomer is an essential part of both catalytic sites. The interface domain is highlighted in color: In the patients of family 1, only the green residues are identical with the wild-type enzyme. The blue residues are replaced by an aberrant sequence, and the red part is completely missing. The atoms of the substrates GSSG and NADPH are indicated as dotted spheres. Note that the nicotine amide ring—otherwise sandwich-like adjacent to the flavin ring—is missing here (1GRA). The structure was created with RasMol V 2.7.2.1.1 (Herbert J. Bernstein, www.bernstein-plus-sons.com/software/rasmol) based on the structural information provided by protein database file 1GRA.¹