structural:expansion, information:extraction
Synthesis

Most animals and plants are able to synthesize vitamin C through a sequence of enzyme -driven steps, which convert monosaccharides to vitamin C. Yeasts do not make l -ascorbic acid but rather its stereoisomer, erythorbic acid. In plants, synthesis is accomplished through the conversion of mannose or galactose to ascorbic acid. In animals, the starting material is glucose. In some species that synthesize ascorbate in the liver (including mammals and perching birds), the glucose is extracted from glycogen; ascorbate synthesis is a glycogenolysis-dependent process. In humans and in animals that cannot synthesize vitamin C, the enzyme l -gulonolactone oxidase (GULO), which catalyzes the last step in the biosynthesis, is highly mutated and non-functional.