2)
NaBH 4 reductions can be carried out in water or alcohol solutions.
The Chemistry of Alcohol Dehydrogenase
- When the enzyme alcohol dehydrogenase converts acetaldehyde to ethanol,
1) ocess by contributing its
2) e is then
NADH acts as a reducing agent by transferring a hydride from C4 of the
nicotinamide ring to the carbonyl group of acetaldehyde.
The nitrogen of the nicotinamide ring facilitates this pr
nonbonding electron pair to the ring, which together with loss of the hydride
converts the ring to the energetically more stable ring found in NAD+.
The ethoxide anion resulting from hydride transfer to acetaldehyd
protonated by the enzyme to form ethanol.
R N
H 2 N
HS O
HR C
O
H
H 3 C
Zn2+
S
S
H+ N
C
H 3 C OH
H HR
N O +
NH 2
HS
R
NAD+
Part of
NADH
+
Ethanol
Cys
His
Cys
re
- Although the carbonyl group of acetaldehyde that accepts the hydride is inherently
1) develops on the oxygen in the
electrophilic, the enzyme enhances this property by providing a zinc ion as a
Lewis acid to coordinate with the carbonyl oxygen.
The Lewis acid stabilizes the negative charge that
transition state.
