Biochemistry: Vitamin B6 and its very important coenzyme form-Pyridoxal phosphate

Vitamin B6 and its family members: Pyridoxine, Pyridoxal & Pyridoxamine.

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Pyridoxine (Vitamin B6)

• Vitamin B₆ contains 3 important members. These only differ from each other by the functional groups attached to each.
• These are all derivatives of Pyridine:

1. Pyridoxine (alcohol)
2. Pyridoxal (aldehyde) and 
3. Pyridoxamine

• The main form of Vitamin B₆ in food is Pyridoxine which is later converted into Pyridoxal and Pyridoxamine in the body.
• Active form of Pyridoxine is Pyridoxal phosphate (PLP).
• It is synthesized by Pyridoxal kinase, utilizing ATP.

Functions of Pyridoxal Phosphate

• The Pyridoxal phosphate (PLP) acts as a coenzyme for many reaction is in amino acid metabolism.
• These are:

1. Transamination
2. Decarboxylation
3. Metabolism of Sulfur containing AA
4. Heme synthesis
5. Production of niacin
6. Glycogenolysis.

1. Transamination

• The Transamination reactions are catalyzed by the Aminotransferases (Transaminases). 
• These reactions need PLP as a coenzyme. 
• Example is: Alanine + Alpha ketoglutarate → Pyruvate + Glutamic acid (Enzyme Alanine transaminase)

2. Decarboxylation

• The decarboxylation reactions require PLP as a coenzyme. 
• Examples are:

1. Glutamate → GABA (inhibitory neurotransmitter) – Vitamin B₆ deficiency may cause convulsions in children.
2. Histidine → Histamine
3. 5-hydroxy tryptophan → Serotonin
4. Cysteine → Taurine
5. Serine → Ethanolamine.

3. Metabolism of Sulfur containing amino acids

• Methionine and Cysteine (sulfur containing amino acids) also require PLP as a …

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