ENZYME CATALYZED OXIDATION

1
ENZYME CATALYZED OXIDATION
2
Lipoxygenase (Lipoxidase)

Detrimental effects.
a.

Destruction of the essential fatty acids.
b.

The free radicals produced damage other compounds
including vitamins and proteins.
c.
Development of off-flavor and odor in beans and
peas
à
a hay-like flavor.
3
Substrate Specificity of Lipoxygenase

• a cis, cis-Penta-1,4-Diene Unit ( CHCH
  CH2 CHCH )
• - Methylene group of the Penta-1,4-Diene Unit to
  be in the ?-8 position.

4
Mechanism of Lipoxygenase Action

• The enzyme forms a stereospecific complex with
  the unsaturated fatty acid.
• 2. The enzyme abstracts either an electron or a
  hydrogen atom stereospecifically from the ?-8
  position producing a free radical at ?-8 of the
  fatty acid.
• 3. The fatty acid free radical isomerizes to
  place the unshared electron at ?-8 causing
  conjugation double bond.
• 4. O2 reacts with the free radical at ?-6 to give
  a peroxy free radical.
• 5. A hydrogen from the medium forms the
  hydroperoxide.

5
Lipoxygenase Oxidation Mechanism
Lipoxygenase Oxidation Mechanism
6
Lipoxygenase Oxidation Mechanism
H
H
H
H
cis
cis
H
H
r
a
n
s
C
C
t
C
C
C
C
C
H
(
C
H
)
C
O
O
H
CH
(CH
)
2
6
C
3
2
4
H
O
O
.
H
H
H
H
cis
cis
H
H
C
C
C
C
trans
C
C
C
H
(
C
H
)
C
O
O
H
2
6
CH
(CH
)
C
3
2
4
H
O
O
H
7
Aldehyde and Alcohol in Tomato from C183 and
C182
Linolenic Acid C
14
O
Lipoxygenase

2
H
O
cis
cis
trans
C
C
C
C
C
C
C
C
C
C
(
C
)
C
O
H
7
O
O
H
O

H
C
C
C
C
C
H
C
cis-3-hexenal
AOR
AOR
O
C
C
C
C
C
H
C
H
H
n-
hexanal
C
C
C
C
C
C
O
H
C
C
C
C
C
C
O
H
H
H
AOR
trans - 2 -
hexenol
cis - 3 -
hexenol
8


H
H
H
C
C
C
C
C
O
H
C
C
C
C
C
C
O
H
C
C
C
C
C
C
O
H
C
H
H
H
n-
hexanol
n -
hexanol
n -
hexanol
AOR
O
C
C
C
C
C
H
C
n -
hexanal
AOR Alcohol
Oxidoreductase
Lipoxygenase
O

2
Linoleic Acid C
14