Vitamin C and copper atoms in their reduced states. Vitamin C acts as an electron donor for eight enzymes: The name "vitamin C" always refers to the -enantiomer of ascorbic acid and its oxidized forms, such as dehydroascorbate (DHA). Therefore, unless written otherwise, "ascorbate" and "ascorbic acid" refer in the nutritional literature to -ascorbate and -ascorbic acid respectively. Ascorbic acid is a weak sugar acid structurally related to glucose. In biological systems, ascorbic acid can be found only at low pH, but in solutions above pH 5 is predominantly found in the ionized form, ascorbate. All of these molecules have vitamin C
Vitamin A Vitamin A Vitamin A is a group of unsaturated nutritional organic compounds that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids (most notably beta-carotene). Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision. Vitamin A is needed by the retina of the eye in the form of retinal, which combines with protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision. Vitamin A also functions in a very different role as retinoic acid (an irreversibly oxidized form of