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Biosyntéza

• Vast majority of animals and plants are able to synthesize vitamin C
• Enzyme-driven steps
• Convert monosaccharides to vitamin C [12]

In plants

• Through the conversion of mannose or galactose

Some animals

• Glucose needed to produce ascorbate in the liver
• Mammals
• Perching birds
• Is extracted from glycogen
• ascorbate synthesis is a glycogenolysis-dependent process [12]

Other more primitive primates (Strepsirrhini)

• Have the ability to make vitamin C [12]

Reptiles and birds

• Biosynthesis is carried out in the kidneys
• Number of species of passerine birds also do not synthesize
• But not all of them
• Ability to synthesize vitamin C
• Presumed to have been lost
• Then later re-acquired in at least two cases [12]

Netopýři

• At least two species of bats
• Frugivorous bat (Rousettus leschenaultii)
• Insectivorous bat (Hipposideros armiger)
• Retain (or regained) their ability of vitamin C production [12]

Guinea pig

• Humans are better than guinea pigs at converting DHA back to ascorbate
• Take much longer to become vitamin C deficient [12]

• In plants, vitamin C is a substrate for ascorbate peroxidase
• Utilizes ascorbate to neutralize toxic hydrogen peroxide (H2O2)
• By converting it to water (H2O) [12]

Lost ability of biosynthesis among the mammals

• All lack the L-gulonolactone oxidase (GULO) enzyme
• Required in the last step of vitamin C synthesis
• Genomes of these species contain GULO as pseudogenes
• Some of these species (including humans)
• Able to live with the lower levels available from their diets
• By recycling oxidised vitamin C [12]

One of two major primate suborders, Haplorrhini

• Simians
• Tarsiers
• Including humans

• Most simians consume the vitamin in amounts 10 to 20 times higher than that recommended by governments for humans
• Discrepancy constitutes much of the basis of the controversy on current recommended dietary allowances
• Countered by arguments that humans are very good at conserving dietary vitamin C
• Are able to maintain blood levels of vitamin C comparable with simians on a far smaller dietary intake
• Perhaps by recycling oxidized vitamin C [12]

Small rodent family Caviidae

• Guinea pigs
• Capybaras
• But occurs in other rodents
• Rats and mice do not need vitamin C [12]

96% of fish (the teleosts)

• Also been lost [12]

Most tested families of bats (order Chiroptera)

• Including major insect and fruit-eating bat families
• Cannot synthesize vitamin C
• A trace of gulonolactone oxidase (GULO)
• Detected in only 1 of 34 bat species tested, across the range of 6 families of bats tested [12]