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Vitamin B6

life science Maturity 11-13 Next article →

Vitamin B6 is an essential nutrient for humans. It belongs to a group of six chemically similar compounds called vitamers.

Pyridoxin
Pyridoxin

These vitamers all share a common core structure known as a pyridine ring. While there are several forms, the most biologically active version is pyridoxal 5′-phosphate (PLP). This molecule acts as a coenzyme, which is a helper molecule for enzymes. It supports more than 140 different chemical reactions within our cells. These reactions are vital for managing amino acids, glucose, and lipids.

Metabolic pathway- pyridoxal 5'-phosphate biosynthesis I v 2.0
Metabolic pathway- pyridoxal 5'-phosphate biosynthesis I v 2.0

Our bodies follow a specific sequence to activate this nutrient. Most people consume pyridoxine (PN) through their diet. Once absorbed, an enzyme called pyridoxal kinase converts pyridoxine into pyridoxamine 5′-phosphate (PMP). Next, other enzymes like pyridoxine 5′-phosphate oxidase transform it into the active PLP form. This second step requires a cofactor called flavin mononucleotide, which comes from vitamin B2.

Pyridoxamin
Pyridoxamin

After the body uses the PLP, it undergoes a non-reversible reaction. It is broken down into 4-pyridoxic acid and excreted through urine.

PLP is a critical worker in several metabolic pathways. In amino acid metabolism, it helps transaminases move amine groups between molecules. This process is essential for creating new amino acids and breaking down others. PLP also helps the body manage selenium by allowing it to be used in selenoproteins. Furthermore, it is required to convert the amino acid tryptophan into niacin.

Pyridoxal2
Pyridoxal2

In terms of energy, PLP is a necessary coenzyme for glycogen phosphorylase. This enzyme helps break down glycogen into glucose to provide energy for the body.

Beyond basic metabolism, B6 plays a major role in our nervous and circulatory systems. It is a necessary cofactor for the biosynthesis of five important neurotransmitters. These include serotonin, dopamine, epinephrine, norepinephrine, and gamma-aminobutyric acid. These chemicals allow our brain to send and receive signals effectively. PLP also aids in the synthesis of hemoglobin, the protein in red blood cells. It even binds to two sites on hemoglobin to improve its ability to carry oxygen.

Plants use vitamin B6 for very different reasons than humans. Plants can synthesize their own pyridoxine to protect themselves from UV-B radiation. High levels of UV-B sunlight can create reactive oxygen species that damage plant tissues. By producing B6, plants can mitigate this damage. Additionally, B6 is necessary for the synthesis of chlorophyll. This is done through an enzyme called aminolevulinic acid synthase. Without enough B6, plants may also suffer from stunted root growth because they cannot make certain hormones.

Because animals cannot make their own B6, we must get it from food. Good sources include beef, pork, fowl, and fish. Dairy, eggs, and various mollusks also contain the vitamin. While deficiency is rare, it can lead to serious health issues. Symptoms can include rashes and inflammation around the eyes and mouth. It can also cause peripheral neuropathy, which affects the nerves in the hands and feet. Some medicines, like the antibiotic isoniazid, can also lower B6 levels in the body.

Health agencies set specific guidelines for how much B6 we should consume. For adults, the recommended daily allowance (RDA) usually falls between 1.0 and 2.0 milligrams. However, there are also safe upper limits to prevent ill effects from overconsumption. These limits vary significantly by country. The United States sets an upper limit of 100 mg per day. In contrast, the European Food Safety Authority sets a much lower limit of 12 mg per day. It is important to note that these risks mostly come from supplements rather than food.

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Pyridoxamin.svg
File:Pyridoxal2.svg
Pyridoxal2.svg
File:Metabolic pathway- pyridoxal 5'-phosphate biosynthesis I v 2.0.svg
Metabolic pathway- pyridoxal 5'-phosphate...
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