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Evolution, huh. Let's go back in time, back when humanoids were able to manufacture their own antioxiedent, namely l-ascorbic acid (vitamin C). At some point in our distant history a mutation occured since then humans have been carrying a defective gene for the production of the liver enzyme, L-gulonolactone oxidase. The pathway of the biosynthesis of ascorbic acid was elucidated at the end of the sixties (Nishikimi and Udenfriend, 1977):
D-glucose =>(1)=> D-glucuronic acid =>(2)=> L-gulonic acid =>(3)=> L-gulonolactone =>(4)=> L-ascorbic acid
Steps 2 and 3 are catalysed by enzymes in the liver. Step 4 is catalysed by L-gulonolactone oxidase, an enzyme in little microsomes. Animals which are scurvy-prone lack this L-gulonolactone oxidase activity
The lack of this enzyme in the human liver produces an inborn error of carbohydrate metabolism which prevents us from synthesising our own ascorbic acid (vitamin C) in our livers. This synthesis is common and normal to all but a very few mammals and they produce large amounts each day. It is a stress-responsive process, and, under stress, mammals produce even greater amounts of ascorbic acid. The main function of this large ascorbic acid production during the evolution of the mammals was to maintain homeostasis during biochemical stress. Because of this defective human gene, man, through out his entire history, has been deprived of this important mammalian protective mechanism.
We evovolved to survive with the mutation, which in and of it's self is pretty cool, because usually a mutation means that you've been selected against.
The only animals on earth that get heart disease are those that don't manufacture their own l-ascorbic acid, humans, guinea pigs, a couple of monkeys and a couple of bats.
Animals that do manufacture their own l-ascorbic acid do so in great volumes, typical l-ascorbic acid production is between 80-180mg/kg. That means a 160 pound man would need somewhere between 6 and 14 *grams* of l-ascorbic acid a day for optimal health. If that 160 pound man had any type of health problem his l-ascorbic acid requirements would skyrocket, 50, 100 grams, just like animals that make their own l-ascorbic acid. 300mg of l-ascorbic acid a day will just keep you from dying of scurvy.
L-ascorbic acid is a stereoisomer, which means there is a mirror image, r-lascorbic acid, when vitamin C is made in a lab, you get both l and r, r is unusable by our bodies, which means when you buy vitamin C and it does not say l-ascorbic acid it means its a racemic, and you are getting both l and r, so a bottle of vitamin C that claim it's 500mg per tablet, you are only getting 250mg of usable vitamin C.
The two people behind the majority of our understanding of l-ascorbic acid are Dr. Irwin Stone, and Dr. Linus Pauling the only two time solo noble prize winner and the father of modern chemistry. Until someone comes along who is a) as smart as Dr. Pauling, b) has the credentials of Dr. Pauling, and c) doesn't have a vested interest one way or the other I'm sticking with Dr. Pauling, and his theories.
If you want to learn more about the biochemistry of l-ascorbic acid, check out my sources for this post:
http://www.seanet.com/~alexs/ascorbate/197x/stone-i-orthomol_psych-1972-v1-n2-3-p82.htm
http://www.whale.to/cancer/stone.html
http://www.science.uva.nl/research/crystallography/franks/collageen/paginas/app1.html
[Posted by: Jay at March 10, 2007 9:33 PM]
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