D-Gulonic acid γ-lactone

L-Gulonolactone (also known as reduced ascorbic acid RAA) is the substrate of the enzyme L-gulono-14-lactone oxidoreductase (EC 1.1.3.8) which catalyzes the last step of the biosynthesis of L-ascorbic acid (vitamin C) in plants and animals. The enzyme L-Gulono-14-lactone oxidase is missing in scurvy-prone vitamin C-deficient animals such as humans. L-Gulonolactone is present in human blood and has been used as one of the markers to compare changes in exercise-induced oxidative stress. (PMID: 16956367 16494601) .