Tuesday, February 27, 2007
Scurvy and Vitamin C
Scurvy is a disease characterized by general lethargy and malaise. As the disease progresses the patient develops pain in the extremities, gingivitis, and ulcerations on the skin. Eventually the skin becomes fragile and starts bleeding, teeth fall out, and arteries and veins burst. Death follows. [OMIM 240400 HYPOASCORBEMIA]
Scurvy is caused by lack of vitamin C (Monday's Molecule #15). Vitamin C (ascorbic acid) can be easily oxidized to dehydroascorbic acid and it is this electron donor property that makes it an important biochemical molecule.
In humans there are about a dozen enzymes whose activity depends on ascorbic acid. The most important ones are the enzymes involved in hydroxylation of proline and lysine during the synthesis of collagen fibers (Collagen). In the absence of proper hydroxylation of these amino acids, the collagen molecules cannot be cross-linked and this leads to weaker skin and weaker lining of blood vessels.
In spite of the fact that ascorbic acid is essential in humans, we cannot synthesize it de novo. We need to get an adequate supply from our food—mostly fruits and vegetables. It was the lack of fresh fruit and vegetables that made scurvy so common in the past. Today the disease is rarely seen, except in alcoholics.
All primates have lost the ability to make ascorbic acid. Some other mammals have independently lost this function; guinea pigs and some fruit-eating bats are the best known examples.