Glycine glyoxylic acid pathway

Besides ascorbic acid, glycine is the most important source of oxalic acid (W5). The metabolic pathway leading from glycine to oxalic acid via glyoxylic acid (which can be readily converted to glycolic acid) and the enzyme systems involved in that pathway have been recently... 

Fig. 4. Scheme showing the pathway leading from glycine to oxalic acid and the other metabolic transformations of glyoxylic acid. 

L-Serine and L-alanine are built from D-glyceric acid 3-phosphate (D 2) by the pathway given in Fig. 166. Glycine is formed from glyoxylic acid which may be... 

Oxalate is a terminal product of normal metabolism. When [ " C]oxalate is injected, most of the labeled compound is excreted, and only a small fraction of the radioactivity is recovered in bone and muscle. There are only two immediate precursors of oxalic acid in normal metabolic pathways glyoxylic acid and 2,3-diketo-L-gulonic acid. The first of these compounds is the product of amino acid oxidation (serine and glycine), and the second is derived from the oxidation of ascorbic acid (see Fig. 3-25). 

Glycine is converted to glyoxylic acid by two different pathways oxidation and transamination. Glycine oxidase, an enzyme found in liver and kidney, deami-... 

A possible pathway of catabolism is through the action of glycine oxidase, which catalyzes the aerobic oxidation only of glycine and sarcosine to yield glyoxylic acid, according to the following equations ... 

Pathway 1 is by the condensation of active formaldehyde and glycine to form serine. The latter can be hydrolytically deaminated to P3rruvic acid. Pathway 2 is by transamination to glyoxylic acid and the oxidation of this... 

Fia. 1. Glycine catabolism pathway 1, via serine and pyruvate pathway 2, via glyoxylic acid and formate pathway 3, via the glycine-succinate cycle. 

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... 

Many of the transaminase reactions are linked to the amination of 2-oxo-glutarate to glutamate or glyoxylate to glycine, which are substrates for oxidative deamination, reforming the oxo-acids, and thus providing a pathway for net deamination of most amino acids. 

The synthesis and interconversion of these amino acids is intimately related to the photorespiratory pathway in plants (Wallsgrove et ai, 1983b). As illustrated in Fig. 2, glycolate, formed in chloroplasts [(1) and (2)], is oxidized to glyoxylate and converted to glycine in peroxisomes [(3), (4), and (5)]. Glycine is,... 

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