Maintains high levels of reduced glutathione in the cytosol. 2 glutathione + NADP(+) = glutathione disulfide + H(+) + NADPH Binds 1 FAD per subunit. Homodimer; disulfide-linked. Each subunit can be divided into 4 domains that are consecutive along the polypeptide chain. Domains 1 and 2 bind FAD and NADPH, respectively. Domain 4 forms the interface. The active site is a redox-active disulfide bond. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.