Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 3 Carbohydrate Metabolism and Its Diseases
(3) Glucose-6-P
NADP
G6P-D
NADPH
(3) 6-P-Gluconate
C*O 2 NADP
6PG-D NADPH
(3) Ribulose-5-P
NADP Nicotinamide adenine
dinucleotide phosphate
TK Transketolase
TA Transaldolase
C*O 2 derived from C 1 of glucose
G6P-D Glucose-6-P Dehydrogenase
6PG-D 6-P-Gluconate Dehydrogenase
FIGURE 3-6 The pentose phosphate
pathway (PPP) or the hexose monophosphate
pathway (HMP). Abbreviations:
NADP , nicotinamide adenine dinucleotide
phosphate; TK, transketolase; TA,
transketolase; TA, transaldolase; C*O 2 , is
derived from C 1 of glucose.
Ribulose-5-P
Glyceraldehyde-3-P
Fructose-6-P
TK
TA
Xylulose-5-P
Sedoheptulose-7-P
Erythrose-4-P
Fructose-6-P
TK
Xylulose-5-P Glyceraldehyde-3-P
6 NADP 6 NADPH
Net: 3 Glucose-6-P
2 Fructose-6-P Glyceraldehyde-3-P 3 CO 2
Glucose-6-P
Glucose-1-P
UTP
P
NAD
UDP-Glucose
NADH
UDP-Glucuronate
Galactose
Glucuronate
NADP
Hexose
Monophosphate
Pathway
L-Ascorbate
GLO
NADPH
L-Gulonate
UTP Uridine triphosphate
NAD Nicotinamide adenine dinucleotide
NADP Nicotinamide adenine dinucleotide phosphate
P Phosphate
NAD
NADH
NADH NAD NADPH NADP
Xylulose-5-P D-Xylulose Xylitol
L-Xylulose
FIGURE 3-7 Glucuronate pathway or the C 6 oxidation pathway. Note that vitamin C is synthesized via this
pathway.
CO 2
acceptor. Oxidized NADP is regenerated from NADPH
via the cytochrome system in the presence of O 2 so the
HMP pathway is an aerobic pathway of glucose oxidation.
Reduced NADPH is also required as a hydrogen donor in
the synthesis of fatty acids. Through generation of NADPH,
the HMP shunt route of carbohydrate metabolism is linked
to that of fat synthesis. Accordingly, glucose oxidation
through the HMP shunt pathway is essential for the synthesis
of fat. In general, the HMP pathway is the major source
of the NADPH, which maintains the reductive environment
for all biosynthetic processes using NADPH as a cofactor.
e . Glucuronate Pathway
This is an alternate pathway of G-6-P oxidation, which has
been named the uronate pathway, the glucuronate pathway,
or the C 6 oxidative pathway. This pathway is shown
in Figure 3-7 . The initial steps of this pathway involve the
formation of uridine diphosphoglucose (UDPG), which,
as noted earlier, is an intermediate in glycogen synthesis.
G-6-P is first converted to G-1-P, which then reacts with
uridine triphosphate (UTP) to form UDPG. This product is
then oxidized at the C 6 position of the glucose moiety in
contrast to the C 1 position, which is oxidized in the HMP