Biochemistry of ascorbic

Buettner GR, Jurkiewicz BA. 1996. Chemistry and biochemistry of ascorbic Acid. In Cadenas E, Packer L, Eds. Handbook of Antioxidants. New York Marcel Dekker, pp. 91-115. 

Levine, M. (19S6). Mew concepts in the biology and biochemistry of ascorbic acid. jV. Engl.. Med. 314,892-902. 

BilgerW andBjorkmanO (1990) Role of the xanthophyll cycle in photoprotection elucidated by measurements oflight-induced absorbance changes, fluorescence and photosynthesis in leaves of Hedera canariensis. Photosynth Res 25 173-185 Bratt CE, Arvidsson P-O, Carlsson M and Akerlund H-E (1995) Regulation ofviolaxanthin de-epoxidase by pH and ascorbate concentration. Photosynth Res 45 169-175 Buettner GR and Jurkiewicz BA (1996) Chemistry and biochemistry of ascorbic acid. In Cadenas E, Packer L (eds) Handbook of Antioxidants, pp 91-115. Marcel Dekker Inc., New York... 

It is beyond the scope of this review to examine the medical evidence in detail some of it has been briefiy reviewed elsewhere (Meiklejohn and Passmore, 1951). But it seems desirable to summarize here the various ways in which current research on the physiology and biochemistry of ascorbic acid is being applied in medical practice. 

Takigami, T., Takeuchi, F., Nakagawa, M., Hase, T. and Tsubaki, M. Stopped-flow analyses on the reaction of ascorbate with cytochrome b561 purified from bovine chromaffin vesicle membranes. Biochemistry 42 8110-8118,2003. 

Dunn JA, Ahmed MU, Murtiashaw MH, Richardson JM, Walla MD, Thorpe SR and Baynes JW (1990) Reaction of ascorbate with lysine and protein under autoxidizing conditions formation of N-(carboxymethyl)lysine by reaction between lysine and products of autoxidation of ascorbate. Biochemistry 29, 10964-10970. 

In the discussion of the biochemistry of copper in Section 62.1.8 it was noted that three types of copper exist in copper enzymes. These are type 1 ( blue copper centres) type 2 ( normal copper centres) and type 3 (which occur as coupled pairs). All three classes are present in the blue copper oxidases laccase, ascorbate oxidase and ceruloplasmin. Laccase contains four copper ions per molecule, and the other two contain eight copper ions per molecule. In all cases oxidation of substrate is linked to the four-electron reduction of dioxygen to water. Unlike cytochrome oxidase, these are water-soluble enzymes, and so are convenient systems for studying the problems of multielectron redox reactions. The type 3 pair of copper centres constitutes the 02-reducing sites in these enzymes, and provides a two-electron pathway to peroxide, bypassing the formation of superoxide. Laccase also contains one type 1 and one type 2 centre. While ascorbate oxidase contains eight copper ions per molecule, so far ESR and analysis data have led to the identification of type 1 (two), type 2 (two) and type 3 (four) copper centres. 

Figure 10.5 Acrylamide and CsCI quenching effects on the ascorbate oxidase emission properties. Steady-state ( ) and dynamic ( ) quenching of ascorbate oxidase by acrylamide (a) and CsCI (b) upon excitation at 293 nm. Source Di Venere, A., Mei, G., Gilardi, G. et al. (1998). European Journal of Biochemistry, 257, 337-343 with permission from Blackwell Publishing Ltd.

Asada, K., Miyake, C., Ogawa, K., and Hossain, M. A., 1996, Microcompartmentation of ascorbate peroxidase and regeneration of ascorbate from ascorbate radical its dual role in chloroplasts, in Plant Peroxidases Biochemistry and Physiology (C. Obinger, U. Burner, R. Ebermann, C. Penel, and H. Greppin, eds.). University of Geneva, pp. 163nl67. 

The observation of L-ascorbic acid 2-0-sulfate, 18, in a number of animal species, including humans, has provoked extensive research into the chemistry and biochemistry of this inorganic ester of ascorbic acid (J, 19,20). Ascorbic acid 2-0-sulfate has been implicated as a biological sulfating agent and proposed as an anticholesteremic agent (21-24). 

Oxidation of the reductone functionality of ascorbic acid is certainly its single most important reaction and results in the formation of its most biologically important derivative, dehydroascorbic acid, 28. As chemistry and biochemistry of dehydroascorbic acid will be covered in a separate section of this volume, only a few of its reactions will be covered here. 

A number of enzymes have been characterized that catalyze reactions involving DHA. In addition, other aspects of DHA biochemistry can be deduced from metabolic studies of ascorbic acid. Experiments demonstrating the biological oxidation of AA and reduction of DHA were first made in 1928 (10) and during the next decade several groups studied these reactions. By 1941 Crook (62) was able to separate the ascorbic acid oxidase and DHA reductase activities and to show that glutathione was used in the reductase reaction. 

Xhe brilliant success of ascorbic acid research in the 1930s led to the commercial production of inexpensive ascorbic acid in large quantities. The wide distribution of ascorbic acid, and its incorporation into many food products, so completely solved the problem of scurvy in both general and special populations that pressure for a more complete scientific understanding of this vitamin was sharply reduced. As a result many questions concerning ascorbic acid s chemistry, biochemistry, physiological roles and kinetics, and its nutritional requirements were deferred for more pressing scientific problems. 

The historical significance of vitamin C was summari/.ed eloquently by the eminent medicinal chemist and pharmacist Professor Ole Glsvold. and the following direct quotation from the 7th edition of this textbook is an appropriate introduction to the signincance of ascorbic acid in medicinal chemistry and ba.sic biochemistry ... 

Sokolova, V. E., Effect of ascorbic acid on the activity of adenosine triphosphatase of heart and skeletal muscle of the guinea pig. Biochemistry (U.S.S.R.) (English translation) 21, 475-478 (1956). 

L-Ascorbic acid is found all over the plant world, often in quite large quantities and distributed throughout the plant. The biochemistry of vitamin C in plants is very poorly understood. view which. seems to be accepted generally is that in some way L-ascorbic acid is merely a secondary product of plant metabolism. It. seems curious that such a ubiquitous compound in plants should be there almost incidentally as a by-product of other proces.ses, though it is fortunate for tho.se creatures that have lost their ability to synthesise the vitamin that it is. so ... 

Messerschmidt, A., Landenstein, R., Huber, R., Bolognesi, M., Avigliano, L., Petruzzelli, R., Rossi, A. and Finazzi Agro, A. 1992. Refined crystal structure of ascorbate oxidase at 1.9 A resolution. Journal of Molecular Biology 224, 179-205. Miki, K., Ezoe, T., Masui, A., Yoshisaka, T., Mimuro, M., Fujiwara-Arasaki, T. and Kasai, N, 1990, Crystallization and preliminary X-ray diffraction studies of C-phycocyanin from a red alga, Porphyra tenera. Journal of Biochemistry 108, 646-649. Molecular Probes. Handbook of fluorescent probes and research chemicals. 1992-1994. 

Bender, D.A. 2003. Vitamin C (Ascorbic acid). In Nutritional Biochemistry of the Vitamins (D.A. Bender, ed.), pp. 357-384. Cambridge University Press, Cambridge. 

Kanauchi, O., Deuchi, K., Imasato, Y, Shizukuishi, M., and Kobayashi, E. 1995. Mechanism for the inhibition of fat digestion by chitosan and for the synergistic effect of ascorbate. Bioscience Biotechnology and Biochemistry 59 786-790. 

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