Glyoxylate oxidase

GO glyoxylate oxidase IMCD inner medullary collecting ducts... 

In the third and final pathway of glycine degradation, the achiral glycine molecule is a substrate for the enzyme D-amino acid oxidase. The glycine is converted to glyoxylate, an alternative substrate for hepatic lactate... 

Glycine oxidase converts glycine to glyoxylic acid according to Equation... 

Figure 8.4. Pathways of tryptophan metaholism. Tryptophan dioxygenase, EC 1.13.11.11 formylkynurenine formamidase, EC 3.5.1.9 kynurenine hydroxylase, EC 1.14.13.9 kynureninase, EC 3.7.1.3 3-hydroxyanthranilate oxidase, EC 1.10.3.5 picolinate carboxylase, EC 4.1.1.45 kynurenine oxoglutarate aminotransferase, EC 2.6.1.7 kynurenine glyoxylate aminotransferase, 2.6.1.63 tryptophan hydroxylase, EC 1.14.16.4 and 5-hydroxytryptophan decarboxylase, EC 4.1.1.26. Relative molecular masses (Mr) tryptophan, 204.2 serotonin, 176.2 kynurenine, 208.2 3-hydroxykynurenine, 223.2 kynurenic acid, 189.2 xanthurenic acid, 205.2 and quinolinic acid 167.1. CoA, coenzyme A.

The purine catabolic pathway appears in Figure 8.31. The end-product of purine catabolism in primates, and in some other vertebrates, is uric acid. Purine catabolism differs in other species. Urate oxidase catalyzes the breakdown of uric acid to allantoin. Allantoin can be further broken down to produce urea and glyoxylate. Allantoin is the purine excretory product in some mammals and reptiles. Urea is the purine excretory product in fish. Guanine is the purine excretory product in pigs and spiders. Uric acid is used for the packaging and excretion of waste N from amino acids in birds and some reptiles. 

Many animals degrade uric acid further (Figure 15.13). Urate oxidase converts uric acid to allantoin, an excretory product in many mammals. Allantoinase catalyzes the hydration of allantoin to form allantoate, which is excreted by bony fish. Other fish, as well as amphibians, produce allantoicase, which splits allantoic acid into glyoxylate and urea. Finally, marine invertebrates degrade urea to NH4 and COz in a reaction catalyzed by urease. 

Figure 16.2-31. Synthesis of glyoxylic acid by glycolate oxidase. The undesired side-reactions (A) with hydrogen peroxide and (B) overoxidation by glycolate oxidase are prevented by in situ formation of an imine.

D-Amino acid oxidase (EC 1.4.3.3) (Eq. (11)), converting glycine to glyoxylate, is present in the CNS (Gaunt and De Duve, 1976), but glycine is a very poor substrate for the enzyme (DeMarchi and Johnston, 1969). 

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