Vitamin C function

Singh A, Kaplan DL (2004) Vitamin C functionalized poly(methyl methacrylate) for free radical scavenging. J Macromol Sci A Pure Appl Chem 41 1377-1386... 

Banhegyi, G., and Loewus, F.A., 2004, Ascorbic acid catabolism Breakdown pathways in animals and plants. In Asard, H., May, J.M., and Smirnoff, N. (eds.), Vitamin C. Functions and Biochemistry in Animals and Plants. BIOS Sci. Publ., London and New York, pp. 31-48. 

Sometimes a coenzyme—a vitamin, a trace element, or a protein-— partners with an enzyme to take part in the lock-and-key pattern of relationship. All water-soluble vitamins— eight B-complex vitamins and vitamin C—function as coenzymes that work together with enzymes. Unless both coenzyme and enzyme are present, no change can be made on the substrate. Metal elements sometimes initiate enzyme reactions. If the metal isn t present, the enzyme doesn t activate. 

All the water-soluble vitamins except vitamin C function as coenzymes. In spite of its name, vitamin C is not actually a vitamin because it is required in fairly high amounts and most mammals are able to synthesize it (Section 22.19). Humans and guinea pigs cannot synthesize it, however, so it must be included in their diets. We have seen that vitamin C and vitamin E are radical inhibitors and therefore are antioxidants. Vitamin C traps radicals formed in aqueous environments, whereas vitamin E traps radicals formed in nonpolar environments (Section 9.8). 

Cofactors assist enzymes in catalyzing a variety of reactions that cannot be catalyzed solely by their amino acid side chains. Cofactors can be metal ions or organic molecules. An enzyme with a tightly bound metal ion is called a metalloenzyme. Cofactors that are organic molecules are called coenzymes and these are derived from vitamins. A vitamin is a substance the body cannot synthesize that is needed in small amounts for normal body function. All the water-soluble vitamins except vitamin C function as coenzymes. Vitamin K is the only water-insoluble vitamin currently recognized to function as a coenzyme. 

Ascorbic Acid A six carbon compound related to glucose. It is found naturally in dtrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a redudng agent and coenzyme in several metabolic pathways. Vitamin C is... 

Jacob, R. A. and Sotoudeh, G. (2002). Vitamin C function and status in chronic disease. Nutr. Clin. Care 5, 66-74. 

Abstract The in vitro enzyme-mediated polymerization of vinyl monomers is reviewed with a scope covering enzymatic polymerization of vitamin C functionalized vinyl monomers, styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible cosolvents. Vitamin C functionalized polymers were synthesized via a two-step biocatalytic approach where vitamin C was first regioselectively coupled to vinyl monomers and then subsequently polymerized. The analysis of this enzymatic cascade approach to functionalized vinyl polymers showed that the vitamin C in polymeric form retained its antioxidant property. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H2O2, initiator fS-diketone) was required for efficient polymerization and that the initiator controls the characteristics of the polymer. The main attributes of enzymatic approaches to vinyl polymerization when compared with more traditional synthetic approaches include facile ambient reaction environments of temperature and pressure, aqueous conditions, and direct control of selectivity to generate functionalized materials as described for the ascorbic acid modified polymers. 

Recently a new strategy was developed whereby a nuld and highly selective enzymatic method was used to covalently couple the primary hydroxyl group of ascorbic acid with styrene and methyl acrylate monomers, followed by a second enzymatic reaction catalyzed by horseradish peroxidase to polymerize the styrene and acrylate monomers yielding vitamin C functionalized... 

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