Chemistry Reference
In-Depth Information
O
COOH
HOOC
H
2
N
61
54
HOOC
Yeasts/
Plants
OH
OH
O
OH
NH
2
NH
2
+
HOOC
HOOC
HOOC
HN
60
63
62
NH
H
2
N
58
OH
OH
H
O
N
HOOC
HN
64
59
O
N
O
H
L-Cysteine
O
OH
O
P
O
H
H
N
N
O
65
HS
O
O
NH
2
N
N
OH
O
O
H
H
N
N
N
N
O
P
O
P
O
HS
O
O
O
O
O
O
P
O
OH
66
O
O
Figure 10.7
Biosynthesis of pantothenate. (
54
), aspartate; (
58
), spermine; (
59
), uracil;
(
60
),
-ketoisovalerate; (
62
), ketopantoate; (
63
), pantoate; (
64
), pantothen-
ate; (
65
), pantetheine 4-phosphate; (
66
), coenzyme A.
β
-alanine; (
61
),
α
linker and phosphorylation of the ribose moiety. Phosphopantetheine can be
attached covalently to serine residues of acyl carrier proteins that are parts of
fatty acid synthases and polyketide synthases.
10.2.8 Vitamin C
Whereas most mammals can synthesize ascorbic acid (vitamin C), (
75
)from
D-glucose 1-phosphate (
67
) via the pathway shown in Fig. 10.8b, humans and
guinea pigs lack the last enzyme of that pathway and are therefore dependent on
nutritional sources (36, 37). Plants use the pathway shown in Fig. 10.8a that has
been elucidated relatively recently (38, 39). Yeasts produce and use a five-carbon
analog, which is called erythroascorbic acid, instead of ascorbate. The biosyn-
thetic pathway of erythroascorbic acid involves the oxidation of D-arabinose to
D-arabino-1,4-lactone, which is then oxidized to erythroascorbic acid.
