Bio-organic Enzyme Mechanisms Flashcards
What types of reactions can enzymes catalyse effectively without the use of a cofactor?
Acid-Base reactions, Charge-Charge interactions and transient covalent bond formation.
What types of reactions does an enzyme need a cofactor for in order for the catalysis to be effective and why?
Redox reactions as most amino acids cannot be oxidised or reduced. Group transfer reactions where the group to be transferred is large, e.g. phosphoryl group.
What reaction is catalysed by pyruvate decarboxylase?
The conversion of pyruvate to acetylaldehyde.
What is the mechanism for pyruvate decarboxylase?
Similar to the E1 mechanism in pyruvate dehydrogenase, using TPP as an electron sink to stabilise the carbanion.
What reaction is catalysed by alcohol dehydrogenase?
The conversion of acetylaldehyde to ethanol.
What is the mechanism for alcohol dehydrogenase?
Hydride transfer from NADH to acetylaldehyde to form an oxyanion, stabilised by zinc ions in the active site. Acetylaldehyde is then protonated by a nearby general acid to form ethanol.
How does alcohol dehydrogenase demonstrate absolute stereospecificity?
The hydride transfer must be from the pro-R hydrogen of NADH to the re face of acetylaldehyde.
What reaction is catalysed by pyruvate carboxylase?
The regeneration of oxaloacetate from pyruvate in gluconeogenesis. USES BIOTIN
What is the mechanism for pyruvate carboxylase?
Phosphate group from ATP is added to pyruvate. Nucleophilic attack of the carbon dioxide by the biotinyl-enzyme. An Sn1 type reaction between pyruvate and the carboxybiotinyl-enzyme, forms pyruvate enolate. Carbon dioxide is transferred to pyruvate enolate, forming oxaloacetate.
What are the features of an E1 elimination mechanism?
Leaving group is removed first.
Carbocation then stabilised (Rate determining step).
What are the features of an E1 conjugate base elimination mechanism?
Base removes proton to from a carbanion.
Leaving group removed.
What are the features of an E2 elimination mechanism?
Concerted process- both bonds are broken at the same time.
What are syn elimination groups?
Groups that leave from the same side of C-C.
What are anti elimination groups?
Groups that leave from opposite sides of C-C.
Where is a Rossman fold found?
In dehydrogenases, such as alcohol dehydrogenase- Arg, Arg, His residues.
