April 21, 2025

Vitamin C is a complex molecule that donates an electron to free metals and then comes apart and cannot be used again. But the only metal that needs an electron is the plus three form of iron, as it is highly reactive and damages nearby molecules. With an added electron, it becomes plus two iron, which is much safer.

Free copper ions are also dangerous to metabolism; but they are controlled by proteins rather than Vitamin C.

It appears that no other metal than iron benefits from Vitamin C; and when other free metals acquire an electron from Vitamin C, they become less functional and somewhat toxic. Zinc is particularly vulnerable to being damaged when picking up an electron from Vitamin C, because it must be exposed to react with foreign matter to break it down.

Animals could originally produce their own Vitamin C by using a few enzymes to convert glucose into Vitamin C. But some animals gave up that ability, as they acquired Vitamin C from plants.

It is not logical or evident that plants would normally use Vitamin C. That's because Vitamin C is an expensive molecule for such a limited purpose. By destroying a glucose molecule, the large amount of ATP that glucose normally produces doesn't get produced.

Yet plants absorb iron in the plus three form from the soil. They use proteins in roots to handle the iron instead of Vitamin C. Plants are chemical factories with a lot of versatility, because they do not need a lot of ATP for motion energy as animals do.

Animals simplify their metabolism to direct it toward producing a lot of ATP for motion. Then they borrow a lot of molecules from plants; and a symbiotic relationship to plants develops, where animals spread seeds and plants keep animals alive for doing so.

Grapes do not have Vitamin C in them, because human selection replaced natural selection; and the Vitamin C that would have been produced for animals disappeared. That's because human selection causes genes to be lost when they are not needed and selected for.

Pineapples do not have Vitamin C in the part that humans eat, though they appear to have Vitamin C around the outer edge, where seeds are sometimes produced.

Squash has no vitamin C in it, because it was totally domesticated by human selection.

The absence of Vitamin C in grapes, pineapples and squash indicates that plants get along just fine without Vitamin C and they only produce it to assist animals.

Why is Vitamin C sometimes listed for grapes and pineapples? Because social deterioration produced rationalizers who try to compensate for their incompetence by guessing. Everything in physics being in error shows how that works. Real procedures would be complicated showing variations and why and where they exist. The test for absence of Vitamin C is zinc gluconate powder not being reduced, which can be tested by tasting.

Animals use Vitamin C for collagen synthesis and a few other things. Collagen is a structural protein. Presumably, Vitamin C prevents plus three iron from damaging the structural protein. Collagen would be more vulnerable to such damage than usual, because breaking protein chains with iron would be much more serious than damaging other types of molecules.

Supposedly, iron gets involved in hydroxylating the protein of collagen; but the descriptions are incoherent in portraying Vitamin C as a catalyst (It's not a catalyst) that supposedly picks up another electron after donating one to iron. That isn't the way metabolism works. Where does the electron come from to restore Vitamin C? Usually from glutathione, which produces an expensive and high energy electron, as glutathione is restored with NADPH, where the electron has the energy equivalent of three ATP molecules.

The most likely explanation is that Vitamin C is doing nothing more than protecting the process of collagen synthesis from damage by plus three iron. The extremely small quantities of Vitamin C that are needed and the expensive glutathione that restores it point to that explanation.

Vitamin C is attached to a protein to hold it in place and conserve small amounts to the maximum extent possible, which is why scurvy takes a long time to show up. That's why such small amounts of Vitamin C and glutathione are needed. If they were actually part of the synthesis of collagen, huge amounts would be required; and that isn't what is happening.

Plants can produce Vitamin C as an expensive molecule a lot easier than animals can; but they would not have been producing it for their own purposes.

Animals originally had two enzymes for producing Vitamin C; and some still do. That means plants were not producing Vitamin C until recently. Animals would not have evolved those enzymes, if Vitamin C were available from plants. Why didn't plants need Vitamin C earlier? It means plants only produced Vitamin C to keep animals alive; not for their own physiology.

People should only take small amounts of Vitamin C, so it isn't damaging zinc or other metals besides iron. Linus Pauling suggested taking large amounts of Vitamin C as supposed cures for diseases; but he was a chemist, not a biologist, and he guessed wrong.

Summary

Vitamin C is not used by plants, because it is high in energy and wasteful. But animals need Vitamin C to protect collagen. It's a last resort and polishing molecule that is seldom needed to prevent free metals from damaging collagen. There is not a lot of free metals in circulation; but if there are, they do too much damage to be allowed near collagen.

So animals evolved two enzymes for synthesizing Vitamin C in small amounts and holds the Vitamin C in place near collagen with another protein, so it is available when needed, because Vitamin C gets broken down easily.

But just as Vitamin C reduces free metals to harmlessness, it reduces zinc to nonfunctionality. So Vitamin C must only exist in small amounts. Cytochrome C can presumably restore zinc by removing the extra electron; but then Cytochrome C needs to get rid of the electron. It can dump it onto hydrogen peroxide, but not a lot of hydrogen peroxide is available.

Zinc is not a strong oxidizing agent; so it can only start the catalytic oxidation of foreign matter when it starts in the plus two form.

Cytochrome C normally exists in the mitochondria for respiration; but a small amount exists in the cytoplasm for unknown reasons. The likely reason is to restore zinc when it gets reduced with an electron.

During early evolution, zinc was so scarce and valuable that restoring it when reduced was extremely important. But that only occurs in minute quantities. When taking supplements of zinc and Vitamin C, the restoring process would get totally overwhelmed.

Over time, plants assisted animals in providing Vitamin C for them as a symbiotic process, which kept animals alive for spreading seeds, because plants can produce exotic chemicals a lot easier than animals can. Animals must direct their physiology toward producing ATP as energy for motion; so they get as much assistance from plants as possible in producing complex molecules such as proteins and vitamins.

In plants, Vitamin C is found where there is green color. It appears that Vitamin C is produced near photosynthesis because of the large amount of energy needed to produce Vitamin C. So Vitamin C is often produced in the skin of fruit but not the rest.