Understand the outline of vitamin C biosynthesis
Vitamin C can be synthesised in some animals, but not in others (like us). Its synthesis begins with glucose 1-phosphate- a 6-membered ring that gets converted into a 5-membered ring further on in the process. Species that lack vitamin C are missing the final reaction in the vitamin C synthesis process.
Vitamin C (ascorbate) can act as a reductant (electron donor) in many reactions, and I'll explore what these processes are throughout this post. Restoration of reduced vitamin C (dehydroascorbate) to ascorbate can also convert reduced glutathione (GSH) into oxidised glutathione (GSSG) at the same time. (GSH and GSSG are also important regulators of oxidation/reduction potentials in cells.)
Vitamin C's role in hydroxyproline production and collagen formation
See previous post: Proteins- Modifications. Conversion of proline to hydroxyproline allows the three strands of collagen to pack closely together. Collagen triple-helices can be crosslinked further in a process requiring lysine and the enzyme lysyl oxidase.
Vitamin C in neurotransmitter synthesis
See previous post: Understanding Neurotransmitters in the CNS. The synthesis pathways involved in making neurotransmitters requires several cofactors, such as B6, Vitamin C, and SAM. Vitamin C reduces Cu2+ to Cu+, which is required for the action of dopamine β-hydroxylase (which converts dopamine to noradrenaline).
Know the daily requirements for vitamin C and disorders related to under supply.
- Children: 35mg/day
- Teenagers: 40mg/day
- Adults: 45mg/day
- Pregnancy: 55mg/day
- Lactation: 80-85mg/day
Sources of vitamin C: capsicum, acerola (West Indian cherry), guava, litchi, oranges, lemons etc. It is readily absorbed and can aid in the absorption of iron.
The most well-known problem with vitamin C deficiency is scurvy. As vitamin C is important in collagen formation, the symptoms of vitamin C are mainly related to collagen breakdown, leading to gingival bleeding, loss of teeth, neuropathy and death. It was a large cause of death among sailors in the 18th century, but is relatively rare in developed countries now.
Understand blood clotting and the indirect involvement of vitamin K
See previous posts:
Vitamin K is required to convert glutamate (Glu) to γ-carboxyglutamate (Gla) via Vitamin K dependent carboxylase. Gla, which binds Ca2+, is necessary for the activation of some of the zymogens (inactive enzymes) in the clotting pathway.
Understand that Vitamin K is chemically similar to vitamin A
Vitamin K has some similarities to vitamin A: both vitamins are fat-soluble, can be derived from plants or bacteria, and have a ring structure with an unsaturated lipid side chain. There are three types of vitamin K: vitamin K1, which is of plant origin; vitamin K2, which is of bacterial origin; and vitamin K3, which is a synthetic form lacking the side chain (only the ring part is required for its action).
Vitamin K dependent reactions
As I mentioned earlier, vitamin K is required to convert Glu into Gla. Throughout this process, vitamin K cycles through several different forms. When Glu is converted into Gla, vitamin K hydroquinone is converted into vitamin K 2,3-epoxide. Vitamin K 2,3-epoxide can be reduced via vitamin K epoxide reductase to form vitamin K quinone, which can be reduced again to re-form vitamin K hydroquinone. Quinones are important in processes such as the electron transport chain.
Vitamin K can also alter Glu in other proteins. One of these is osteocalcin, a protein found in osteoblasts. As osteocalcin is only found in osteoblasts, it is a useful marker for bone mineralisation and calcification. Matrix Gla protein can also regulate bone mineralisation and calcification, but it is not unique to osteoblasts.
Know the daily requirements for vitamin K and disorders related to under supply.
- Children: 25-35 μg/day
- Teenagers: 45-55 μg/day
- Men: 70 μg/day
- Women: 60 μg/day
Vitamin K1 is found in parsley, green leafy vegetables, spices and broccoli, whereas vitamin K2 is found in chicken and prepared meats. Vitamin K is lost fairly rapidly so you do need to keep up your intake. Another issue with vitamin K is that very little of it is found in newborns, and not much is passed down through breast milk. In some babies, haemorrhagic disease (which comes with a risk of brain bleed) may be an issue due to low vitamin K, so vitamin K injections are routinely offered at birth. Vitamin K may also be deficient in patients who have a blockage in their bile ducts, as bile salts are required for vitamin K absorption.
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