Aminotransferase Mechanism Flashcards
What type of kinetics is aminotransferase an example of?
Bi-Bi ping-pong kinetics.
How is glutamate synthesised?
From α-KG and ammonia de novo.
How can other chiral amino acids be synthesised?
By transamination- stereospecific transfer of the amino group in glutamate to the α carbon.
What are the two main stages involved in transamination?
- Conversion of an amino acid to α-keto acid.
2. Conversion of an α-keto acid to an amino acid.
What are the 3 steps involved in each of the stages of transamination?
- Transimination
- Tautomerization
- Hydrolysis
What is an aldimine?
A schiff base that has formed between an imine and aldehyde.
What is a ketimine?
A schiff base that has formed between an imine and a ketone.
How is PLP attached to the aminotransferase?
Covalently attached to the ɛ-amino group of a lys residue in the active site.
What allows PLP to act as a mobile electron sink?
Its stable tautomeric forms.
Describe transimination (1).
Nucleophilic attack of the enzyme-PLP schiff base, forming aldimine and releasing the lys residue.
Describe tautomerization (2).
Lys acts as a general base and abstracts a proton, forming a carbanion- stabilised by PLP.
Amino acid-PLP schiff base tautomerises to an α-keto acid-PMP schiff base via a resonance stabilised quinonoid intermediate.
Decribe hydrolysis (3).
α-keto acid-PMP schiff base is hydrolysed to give PMP and α-keto acid 1.
Describe transimination (1’).
Nucleophilic attack of the enzyme-PMP schiff base to form ketimine and release the lys residue.
Describe tautomerisation (2’).
α-keto acid-PMP schiff base tautomerises to form an amino acid-PLP schiff base.
Describe hydrolysis (3’).
ɛ-amino group of lys attacks the amino acid-PLP schiff base, regenerating the enzyme-PLP schiff base and forming amino acid 2.