The last step of the biosynthesis ofl-ascorbic acid (vitamin C) in plants and animals is catalyzed by l-gulono-1,4-lactone oxidoreductases, which use bothl-gulono-1,4-lactone and l-galactono-1,4-lactone as substrates. l-Gul-ono-1,4-lactone oxidase is missing in scurvy-prone, vitamin C-deficient ani-mals, such as humans and guinea pigs, which are also highly susceptible to tuberculosis.