TAILIEUCHUNG - Báo cáo khoa học: Vitamin C Biosynthesis, recycling and degradation in mammals

Vitamin C, a reducing agent and antioxidant, is a cofactor in reactions cata-lyzed by Cu + -dependent monooxygenases and Fe 2+ -dependent dioxygenas-es. It is synthesized, in vertebrates having this capacity, fromd-glucuronate. The latter is formed through direct hydrolysis of uridine diphosphate (UDP)-glucuronate by enzyme(s) bound to the endoplasmic reticulum mem-brane, sharing many properties with, and most likely identical to, UDP-glucuronosyltransferases. | IFEBS Journal REVIEW ARTICLE Vitamin C Biosynthesis recycling and degradation in mammals Carole L. Linster and Emile Van Schaftingen Université Catholique de Louvain Christian de Duve Institute of Cellular Pathology Brussels Belgium Keywords ascorbate dehydroascorbate 2 3-diketogulonate glucuronate gulonolactonase L-gulonolactone oxidase semidehydroascorbate UDP-glucuronosyltransferases vitamin C xenobiotics Correspondence E. Van Schaftingen Laboratory of PhysiologicalChemistry UCL-ICP Avenue Hippocrate 75 B-1200 Brussels Belgium Fax 32 27647598 Tel 32 27647564 E-mail vanschaftingen@ C. L. Linster The Department of Chemistry and Biochemistry and the Molecular Biology Institute University of California Los Angeles CA 90095-1569 USA Fax 1 310 825 1968 Tel 1 310 825 3137 E-mail linster@ Received 12 September 2006 revised 1 November 2006 accepted 21 November 2006 doi Vitamin C a reducing agent and antioxidant is a cofactor in reactions catalyzed by Cu -dependent monooxygenases and Fe2 -dependent dioxygenases. It is synthesized in vertebrates having this capacity from D-glucuronate. The latter is formed through direct hydrolysis of uridine diphosphate UDP -glucuronate by enzyme s bound to the endoplasmic reticulum membrane sharing many properties with and most likely identical to UDP-glucuronosyltransferases. Non-glucuronidable xenobiotics aminopyrine metyrapone chloretone and others stimulate the enzymatic hydrolysis of UDP-glucuronate accounting for their effect to increase vitamin C formation in vivo. Glucuronate is converted to L-gulonate by aldehyde reductase an enzyme of the aldo-keto reductase superfamily. L-Gulonate is converted to L-gulonolactone by a lactonase identified as SMP30 or regucalcin whose absence in mice leads to vitamin C deficiency. The last step in the pathway of vitamin C synthesis is the oxidation of L-gulonolactone to L-ascorbic acid by L-gulonolactone oxidase an enzyme associated .

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