L-gulono-y-lactone

L-Ascorbic acid, better known as vitamin C, has the simplest chemical structure of all the vitamins (Figure 18.30). It is widely distributed in the animal and plant kingdoms, and only a few vertebrates—humans and other primates, guinea pigs, fruit-eating bats, certain birds, and some fish (rainbow trout, carp, and Coho salmon, for example)—are unable to synthesize it. In all these organisms, the inability to synthesize ascorbic acid stems from a lack of a liver enzyme, L-gulono-y-lactone oxidase. 

Various y-lactones derived from carbohydrates have found use as antioxidants. For example, the 2,3- and 5,6-sulfinyl-L-gulono-y-lactones (179) and (180) may be used as preservatives in lubricating oils, foodstuffs, and a variety of other substances <93EUP552651>. 

Abbreviations used in this chapter bp, base pairs FAD, flavine adenine dinucleotide GLO, L-gulono-y-lactone oxidase ODS rat, osteogenic disorder Shionogi rat UDPGT, uridine diphosphate glucuronosyl-transferase. 

This reaction is considered to be catalyzed by NADPH-dependent D-glucuronate reductase, the enzyme that acts on D-glucuronic acid in the other pathway. For the formation of L-gulono-"y-lactone, Chatterjee et al. (1961) proposed the presence of a different enzyme attacking D-glucurono-7-lactone with the requirement of cyanide, but their proposal was later challenged (Sato et al., 1976). 

Xenobiotics UDP glucose dehydrogenase UDP glucuronosyl-transferase UDP glucuronic acid pyrophosphatase P-Glucuronidase L-Gulono-y-lactone oxidase... 

GLO catalyzes the following reaction L-gulono-y-lactone + 02- L-ascor-bic acid + H2O2 (Kiuchi et al., 1982). 2-Keto-L-gulono-7-lactone is formed primarily and is spontaneously converted to L-ascorbic acid by enolization. 

Kawai, T., Nishikimi, M., Ozawa, T., and Yagi, K., 1992, A missense mutation of L-gulono-y-lactone oxidase causes the inability of scurvy-prone osteogenic disorder rats to synthesize L-ascorbic acid, J. Biol. Chem. 267 21973-21976. 

Nakagawa, H., Asano, A., and Sato, R., 1975, Ascorbate-synthesizing system in rat liver microsomes II. A peptide-bound flavin as the prosthetic group of L-gulono-y-lactone oxidase, J. Biochem. (Tokyo) 77 221-232. 

Nishikimi, M., and Udenfriend, S., 1976, Immunologic evidence that the gene for L-gulono-y-lactone oxidase is not expressed in animals subject to scurvy, Proc. Natl. Acad. Sci. USA 73 2066-2068. 

Sugisawa, T., Ojima, S., Matzinger, R, et al. (1995). Isolation and Characterization of a New Vitamin C Producing Enzyme (L-gulono-y-lactone Dehydrogenase) of Bacterial Origin, Biosci. 

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