Biomedical Engineering Reference
In-Depth Information
6-phosphate residues present in the oligosaccharide side-chains of the enzyme. Mannose-6-phos-
phate receptors are found on the surfaces of various cell types, and also intracellularly, associated
with the golgi complex, which then directs the enzyme to the lysosomes.
The enzyme urate oxidase has also found medical application for the treatment of acute hype-
ruricaemia (elevated plasma uric acid levels), associated with various tumours, particularly during
their treatment with chemotherapy.
Uric acid is the end-product of purine metabolism in humans, other primates, birds and rep-
tiles. It is produced in the liver by the oxidation of xanthine and hypoxanthine (Figure 12.16),
Purine nucleotides
GMP/AMP
Ribose
Pi
O
O
N
N
H
H
N
Xanthine oxidase
N
OH
N
H
N
H
N
HO
HO
N
Uric Acid
Xanthine
(Excreted by many primates,
birds, reptiles and insects)
Urate
oxidase
O
O
H
N
NH
2
C
Allantoinase
NH
2
C
NH
2
O
C
O
C
C
H
Urea
N
H
N
H
Allantoin
(Excreted by amphibians
and some fish)
(Excreted by most mammals)
NH
4
+
ammonium ion
(Excreted by marine
invertebrates)
Figure 12.16
Summary overview of purine metabolism
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