1 (139)

Prévia do material em texto

S-152 Chapter 13 Bioenergetics and Biochemical Reaction Types
�
Glyceraldehyde
3-phosphate
Erythrose
4-phosphate
Fructose
6-phosphate
transaldolase
O
C
�
H
C
CH2OPO3
2�
H OH
CH OH
C
CH2OPO3
2�
H OHC
CH2OPO3
2�
H OH
C
O H
CH OH
CHO H
Sedoheptulose
7-phosphate
CH OH
CH OH
C
CH2OPO3
2�
H OH
CHO H
CH2OH
C O CH2OH
C O
18. Enzymatic Reaction Mechanisms II Biochemical reactions often look more complex than they
really are. In the pentose phosphate pathway (Chapter 14), sedoheptulose 7-phosphate and glycer-
aldehyde 3-phosphate react to form erythrose 4-phosphate and fructose 6-phosphate in a reaction
catalyzed by transaldolase.
�O
O
N
HH
:
C
O
NH2
NADH
NAD+
L-Lactate
Pyruvate
CH3
H+
R
H
N
+
R
C
O
NH2 +
C O
C
�OO
C
C
H
OHCH3
Draw the mechanism of this reaction (show electron-pushing arrows). (Hint: This is a common reaction
throughout metabolism; the mechanism is similar to that catalyzed by other dehydrogenases that use
NADH, such as alcohol dehydrogenase.)
Answer The mechanism is the same as that of the alcohol dehydrogenase reaction
(Fig. 14–13, p. 547).
Draw a mechanism for this reaction (show electron-pushing arrows). (Hint: Take another look at aldol
condensations, then consider the name of this enzyme.)
2608T_ch13sm_S142-S159 02/21/2008 7:16 pm Page S-152 pinnacle OSX:Desktop Folder:TEMPWORK:FEBRUARY:21-02-08:WHQY028/soln: