Vitamin C, also known as ascorbic acid, is a water-soluble vitamin synthesized from glucose. It is only a vitamin for animals that have lost the enzyme Gulonolactone Oxidase, which is the last step in ascorbate synthesis. These animals include primates, bats, guinea pigs and perching birds. The reaction is:
Functions Vitamin C functions mainly as an antioxidant by sacrificing itself in order to prevent the oxidation of other molecules. Vitamin C helps to form collagen, which strengthens blood vessel walls, forms scar tissue, and provides a matrix for bone growth. Vitamin C also aids in the metabolism of amino acids and thyroxin synthesis, along with aiding in the absorption of iron. Many believe that vitamin C also aids in the body’s ability to fight off a cold. Although this has not been completely proven, research has shown that vitamin C does increase the body’s immune defenses.
Ascorbate is involved in 2 general types of reactions, all of which involve hydroxylation using molecular oxygen:
1. Monooxygenase: are dependent upon Cu++, O2
ex: Norepinephrine synthesis, peptide hormone amidation
· Norepinephrine synthesis in the adrenal medulla: Dopamine + O2 + ascorbate, + Cu+ Norepinephrine + H2O + dehydroascrobate + Cu++
· Peptide hormone amidation: Peptide-(glycine) peptide-NH2 + glyoxylate (CHO-CHOOH)
Includes: CCK, vasopression, gastrin releasing factor, gastrin, melanotropin, growth hormone release factor, MSH, corticotropin and calcitonin.
2. Dioxygenases: are dependent upon Fe++, O2, and a-ketoglutarate ex: carnitine synthesis, tyrosine degradation, hydroxylation of collagen
· Hydroxylation of proline and lysine in collagen:
This is found on many proteins of the extracellular matrix (collagen, elastin), as well as on C1q component of the complement, and maybe on acetylcholinesterase. The function of the ascorbate here, like that of the monooxygenase reactions, is to serve as a reducing agent for the Fe++ used in the reaction. It is the failure of hydroxylate collagens that leads to survey.
· Tyrosine Degradation (4-hydroxyphenyl pyruvate dioxygenase):
Decreased ascorbate levels results in decreased muscle carnitine levels, and thus decreased oxidation of fatty acid in the mitochondria. Muscle synthesized on the protein and released as such upon protein degradation; it is found on proteins such as histones, calmodulin, myosin, cytochrome c. Overall, if you decrease vitamin C, you will have a decrease in carnitine and subsequently a decrease in beta-oxidation and thus the muscle must rely on other energy forms because it is not able to transfer fatty acids efficiently into the mitochondria.
Deficiency Scurvy is the name given to someone who severely lacks vitamin C. Acknowledgement of scurvy symptoms dates back to the Papryrus of Elber, Egypt, in approximately 1550 BC. Documentation of scurvy symptoms also exist during the explorations of Jacques Cartier in 1535. It was at this time that Native Americans taught Cartier to use white cedar extract in treat his sailors that were dying from scurvy. At the time, no one knew exactly what was causing this, until a British physician decided to conduct a study that provided a few sailors with lime juice. Those who consumed the lime juice did not develop scurvy, thus giving them the nickname “limeys.” Eventually the factor was isolated from the lime juice and found to be the 6-carbon glucose structure termed ascorbic acid (vitamin C).
Symptoms include microcytic anemia, hemorrhaging, bleeding gums, muscles begin to degenerate, joint pain, and failure of wounds to heal. Vitamin C, though, is readily reversible by taking moderate dosages of the vitamin.
Symptoms of scurvy: o Soft bones (loss of collagen matrix, maybe loss of sulfonation) o Gum bleeding, teeth loosening (loss of cell matrix) o Capillary bleeding (loss of extracellular matrix supporting capillaries) o Slowed wound healing (is dependent on collagen and the extracellular matrix) o Coiled hair (changes in collagen structure in the hair) o Psychosis, hysteria, depression (?? Loss of neurotransmitters??)
Individuals are at risk for developing a vitamin C deficiency with an increased intake of steroid or aromatic drugs. These increase the need for ascorbate to hydoxylate and remove the compounds from the body. Examples of these types of drugs include: oral contraceptives, toxins, barbituates and stress-related glucocorticoids.
Individuals who smoke cigarettes also have a high requirement for vitamin C. These individuals have a significantly lower serum concentration. This is believed to be due to the toxins in the smoke that promote dangerous oxidation and free radical reactions in the lungs and body; prevention and correction of these reactions depletes the body of ascorbate. Smokers are recommended to increase their ascorbate intake to 100 mg/day.
Toxicity Even though vitamin C is a water soluble vitamin, supplementing with excessive vitamin C can be dangerous. In certain individuals high doses can cause iron toxicity due to its mobilization effect.
Sources o citrus fruits (i.e. oranges, kiwi, and mangoes) o cabbage-type vegetables (i.e. spinach) o dark green vegetables (i.e. broccoli, snow peas, and brussels sprouts) o papayas o cantaloupe o strawberries o red bell peppers o lettuce o tomatoes o potatoes