Elementary plant Biochemistry and Biotechnology (2+1)

Pyridoxine

• The coenzyme form of pyridoxine is known as pyridoxal phosphate (PP).
• The most common type of reaction requiring PP as a coenzyme is transamination.
  
• Enzymes catalysing such reactions are known as transminases of aminotransferases.
  
• The coenzyme binds to its apoenzyme via Schiffs base between its aldehyde group and the epsilonamino group of a lysine in the enzyme.
• Additional ionic bond is also formed between its phosphate and the enzyme.
• During reaction,α-amino group of amino acid displaces the epsilon amino group forming a new Schiff’s base. By a series of electron shifts and rearrangements, the pyridoxal phosphate becomes pyridoxamine phosphate.
• The amino acid is oxidatively deaminated to form the corresponding α-keto acid to change it to an amino acid.
• PP also acts as coenzyme in the decarboxylation, desulfuration, transulfuration reactions associated with amino acid metabolism.