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Ascorbate (vitamin C) is an important antioxidant and an enzyme cofactor. It is synthesized via two routes in plants: L-Galactose pathway; and L-Gulose pathway. The pathway showed here is L-Galactose pathway and also known as Smirnoff-Wheeler pathway (Wheeler et al., 1998). All the enzymes of this pathway are cytosolic except the L-galctonolactone dehydrogenase (GLDH), which catalyzes last reaction (L-galactono-1,4-lactone --> ascorbate). GLDH is located on inner mitochondrial membrane (Wheeler et al., 1998; Bartoli et al., 2000). According to Bartoli et al., 2000, L-galactono-1,4-lactone may diffuse through the outer mitochondrial membrane, which is highly permeable, while a specific ascorbate transporter may be required for transport across the inner membrane, which is selectively permeable. As GLDH spans the inner mitochondrial membrane, no transporters would be required, since the catalytic site of GLDH faces the intermembrane space (Bartoli et al., 2000).
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