ofonorow wrote:
1. Why did biochemist/exert Sherry Lewin write in Vitamin C: Its Biology and Medical Potential that vitamin C traveled in the blood as ascorbic acid? (And as SA in the lymph?)
The statement "vitamin C travels in the blood as ascorbic acid" is true only as long as it does not mean "vitamin C travels in the blood only as ascorbic acid." Sodium ascorbate circulates in the blood as the result of ascorbic acid reacting with sodium bicarbonate in the blood, or as the result of sodium ascorbate being absorbed into the bloodstream from the digestive tract. Furthermore, it is well known that dehydroascorbic acid is present in the blood, because that is the form of vitamin C than can be transported into cells by means of glucose transporters, whereas ascorbate cannot.
ofonorow wrote:
2. Why did Cathcart report that he could only achieve the 'ascorbate effect' orally, with ascorbic acid?
I can only guess at the answer to that question. It may be that ascorbic acid is more rapidly absorbed from the digestive tract than sodium ascorbate. I recall reading that ascorbic acid can be absorbed into the bloodstream directly from the stomach, and that vitamin C is aborbed from the small intestine by means of sodium-dependent transporters. For that reason, I would expect that sodium ascorbate is more readily absorbed than ascorbic acid from the small intestine, but ascorbic acid may be more rapidly absorbed from the stomach. I doubt the "ascorbate effect" depends on ascorbic acid entering the bloodstream, because in that case, it could not be attained by intravenous administration of sodium ascorbate.
ofonorow wrote:
3. Why would vitamin C and glucose 'compete' for entry into cells? (Ely's GAA theory)
Dehydroascorbic acid is chemically similar to glucose, so it can use the same cellular transport mechanism. There is competition because cells have limited capacity and a limited number of glucose transporters. To draw an analogy, let men represent dehydroascorbic acid and women represent glucose. Suppose there are 50 men waiting for a bus. An empty bus arrives, and all 50 men can board. Now suppose there are 50 men and 50 women waiting for the same bus. When the bus arrives, in a non-Islamic country, the people queue up without regard to gender. In that case, it is possible the bus will be filled to capacity before all 50 men have boarded.
ofonorow wrote:
4. And I still don't understand how donating an electron "changes the molecule" so that it can use the GLUT receptor. Why couldn't AA use the GLUT receptor?
It is probably because dehydroascorbic acid is chemically more similar to glucose than ascorbic acid or ascorbate is. The oxidation of ascorbic acid to dehydroascorbic acid results in a different molecule, having a different chemical formula. Ascorbic acid is C6H8O6, and dehydroascorbic acid is C6H6O6; it has lost two hydrogen atoms. In the process of donating two electrons, ascorbic acid also loses two hydrogen nucleii, so the chemical formula changes. In the case of sodium ascorbate, it donates two electrons and loses one hydrogen nucleus and one sodium nucleus, becoming dehydroascorbic acid, converting from a neutral salt back to an acid.
It is enlightening to go to Wikipedia and compare the molecular diagrams of ascorbic acid, sodium ascorbate, and dehydroascorbic acid. The differences occur at the bottom side of the pentagon at the bottom of the molecule, while the rest of the molecule remains the same. The corners of the pentagon represent carbon atoms, which each have four bonds with neighboring atoms. In the case of ascorbic acid, the bottom two carbon atoms have a double bond with each other, each has a single bond to an upper carbon atom in the pentagon, and each has a bond extending down to an OH (hydroxyl) group. In the case of sodium ascorbate, one of the lower OH groups has the H replaced by Na, which is sodium. In the case of dehydroascorbic acid, the bottom two carbon atoms have a single bond with each other, and each has a double bond extending down to an oxygen atom; the two hydrogen atoms (or hydrogen atom and sodium atom) are gone.
ofonorow wrote:
One scenario might be that "Free" AA does rapidly break down into DHA in the blood (that which doesn't attach to sodium) and this resulting DHA uses the GLUT transporters as reported. However, Sherry Lewin also notes that DHA is short-lived, and further breaks down quickly into substances that can not be recyled back into vitamin C.
I suspect that is the case, but note that either ascorbic acid or sodium ascorbate can be doubly oxidized to dehydroascorbic acid. The oxidation likely occurs as the result of both ascorbic acid and sodium ascorbate quenching free radicals in the blood. It seems that ascorbic acid probably has a short life span in the blood, as it can quench a free radical directly, or it can react with sodium bicarbonate, becoming sodium ascorbate, which then quenches a free radical. I suspect that there is a need for both ascorbic acid and sodium ascorbate in the blood, involving different reactions with free radicals.
ofonorow wrote:
Steve, is there an experiment that could be run in water to test the idea that "free" AA will combine with sodium, and verify how much, etc?
There probably is. We know from experience that when you combine ascorbic acid with sodium bicarbonate in water, a fizzing reaction occurs in which the ascorbic acid molecule gives up an H and takes an Na from the sodium bicarbonate molecule. Carbon dioxide and water are byproducts of the reaction, and the pH of the solution is raised (the acid is converted to a salt). If the solution is dilute, the reactions proceed at a slower rate, while unreacted reactants remain in solution. Blood is a fairly dilute solution of sodium bicarbonate, compared to the concentration we use in a container to make sodium ascorbate, but the concentration of ascorbic acid in blood is far lower than the concentration of sodium bicarbonate. Whenever there is an overabundance of one reactant in a solution, it tends to scavenge all of the other reactant. An experiment in water could be set up that simulates the concentrations of sodium bicarbonate and ascorbic acid in blood. Measuring the pH of the solution would be only a first step in analyzing the result, but I would expect it to be at or near normal physiologic pH. The relative concentrations of ascorbic acid and sodium ascorbate could be ascertained by very accurate pH measurement and complex calculations. One could check for carbon dioxide. If bubbles are visible, that would be a certain indicator of the reaction. There are probably other techniques that could be used to corroborate the results.