438
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
phate plus other analogs of pentose phosphate.* It is clear that, although
the calculations differ slightly in the different systems cited, there exists
a ready equilibrium which not only may permit an interchange of
HC=0
1
HC—OH
|
[O—C —H
1
H —C—OH
1
H—C—OH
1
1
H 2 COP
G-6-P
H 2 C—OH
c=o
1
1
H —C—OH
^
1
H —C —OH
1
1
H—C—OP
1 1
H
Ru-5-P
I
PKPE
>
i
H—C—OH
1
1
c=o
1
HO—C—H
1
H—C—OH
1
H—C—OP
H
Xu- 5-P
4
5
6
PPI
2
3
4
5
6
T
+
HC = 0
1
1
H —C —OH
1
1
H —C —OH
1
-"
1
H —C —OH
1 1
H —C —OP
1
1
H
R-5-P
B
c
+ D
E
F
R-5-P
1
2
3
B
c —>■ —>■
D etc.
E (Fig. 2)
F
GLA-P
SH-7-P
FIG. 4. The pentose phosphate isomerase (PPI) and phosphoketopentose epimerase (PKPE) reactions.
added hexose into xylulose phosphate, but also can admit pentoses into
the scheme, as in Lactobacillus pentosus (105). Together with the
activities of transketolase and transaldolase enzymes (see below), this
* Tabachnik et al. y working with spinach and rabbit tissue enzymes, have calculated 47.7% R-5-P, 14.6% Ru-5-P, and 43.8% Xu-5-P (104) at equilibrium.
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
phate plus other analogs of pentose phosphate.* It is clear that, although
the calculations differ slightly in the different systems cited, there exists
a ready equilibrium which not only may permit an interchange of
HC=0
1
HC—OH
|
[O—C —H
1
H —C—OH
1
H—C—OH
1
1
H 2 COP
G-6-P
H 2 C—OH
c=o
1
1
H —C—OH
^
1
H —C —OH
1
1
H—C—OP
1 1
H
Ru-5-P
I
PKPE
>
i
H—C—OH
1
1
c=o
1
HO—C—H
1
H—C—OH
1
H—C—OP
H
Xu- 5-P
4
5
6
PPI
2
3
4
5
6
T
+
HC = 0
1
1
H —C —OH
1
1
H —C —OH
1
-"
1
H —C —OH
1 1
H —C —OP
1
1
H
R-5-P
B
c
+ D
E
F
R-5-P
1
2
3
B
c —>■ —>■
D etc.
E (Fig. 2)
F
GLA-P
SH-7-P
FIG. 4. The pentose phosphate isomerase (PPI) and phosphoketopentose epimerase (PKPE) reactions.
added hexose into xylulose phosphate, but also can admit pentoses into
the scheme, as in Lactobacillus pentosus (105). Together with the
activities of transketolase and transaldolase enzymes (see below), this
* Tabachnik et al. y working with spinach and rabbit tissue enzymes, have calculated 47.7% R-5-P, 14.6% Ru-5-P, and 43.8% Xu-5-P (104) at equilibrium.