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772 Chapter 23
Copyright © 2017 Pearson Education, Inc.
36.
CH
2
N
H
HC
N
+
NH
3
+
N
H
HC
N
CH
2
E
1
/PLP
transimination
S S
E
2
N
H
HC
CH
2
+
S SH
+
CO
2
S SH
H
2
NCH
2
HS SH
S S
E
3
THF
+
+
ΝΗ
4
+
+
,
N
10
-methylene-THF
H
+
FADH
2
+
FAD
E
4
FAD
N
5
NADH
NAD
+
_
O
C
O
CH
2
O
C
O
N
transimination
E
(CH
2
)
4
NH
2
N
HC
N
C
CH
3
CH
H
+
C
O
O
_
glycine
37.
Nonenzyme-bound FAD is a stronger oxidizing agent than
NAD
+
, so
NAD
+
cannot oxidize FADH
2
to
FAD. When the enzyme binds FAD, it makes it a weaker oxidizing agent. Therefore, when bound to the
enzyme, FAD is a weaker oxidizing agent than
NAD
+
, so
NAD
+
can oxidize enzyme-bound FADH
2
to
enzyme-bound FAD.