Chapter 6 - Vitamin C

Abstract

Publisher Summary This chapter provides an overview of vitamin C. Vitamin C is widely distributed in nature in both plant and animal tissues. It is a water-soluble monosaccharide, occurring in the reduced and oxidized forms known as ascorbic acid and dehydroascorbic acid, respectively. Tissues with a high vitamin C content include the pituitary, adrenals, the lens and aqueous and vitreous humors of the eye, the intestines, and the white blood cells. Tissues with a relatively low vitamin C content are the brain, muscles, and red blood cells. The vitamin is synthesized within the animal body from glucuronic acid, which is first converted to L-gulonic acid in a reaction that requires reduced nicotinamide adenine dinucleotide (NAD) as cofactor. The gulonic acid is then converted via L-gulonic acid lactone and 2-keto-L-gulonolactone to ascorbic acid. The last step in the conversion cannot be undertaken by animals that lack the required enzyme. These include man, other primates, the Indian fruit bat, and the guinea pig. Most other animals possess the necessary enzyme for vitamin C synthesis and for them ascorbic acid—although essential—is not a vitamin. It is interesting that the agouti, which is closely related to the guinea pig is able to synthesize its own vitamin C. When vitamin C is lacking in the diet, depletion of the tissues is slow in man, but relatively rapid in the guinea pig, in which scurvy can be induced in three to four weeks. The guinea pig has the highest requirement for vitamin C, relative to its weight, of any of the mammals so far investigated.