Glycine metabolism

Durre P, JR Andreesen (1983) Purine and glycine metabolism by purinolytic Clostridia. J Bacteriol 154 192-199. 

MECHANISM RGURE 18-20 Interplay of the pyridoxal phosphate and tetrahydrofolate cofactors in serine and glycine metabolism. The... 

Reorganizes coverage of amino acid degradation to focus on the big picture Adds new material on the relative importance of several degradative pathways Includes a new description of the interplay of the pyridoxal phosphate and tetrahydrofolate cofactors in serine and glycine metabolism... 

Role of Pyridoxal Phosphate in Glycine Metabolism The enzyme serine hydroxymethyltrans-ferase requires pyridoxal phosphate as cofactor. Propose a mechanism for the reaction catalyzed by this enzyme, in the direction of serine degradation (glycine production). (Hint see Figs 18-19 and 18-20b.)... 

Figure 20.15 Interrelationships between the serine and glycine metabolic pathways. FH4-"C" indicates 5,10-methylenetetrahydrofolate. (Adapted from Yoshida T, Kikuchi G. Comparative study on major pathways of glycine and serine catabolism in vertebrate livers. ) Biochem 72 1503-1516, 1972.)...

Halton, D. M., and Krieger, 1. (1980). Studies of glycine metabolism and transport in fibroblasts from patients with nonketotic hyperglycinemia. Pediair. Res. 14,932-934. 

D hW, in xenobiotic conjugate identification was found, presumably because large samples are required. 2-D NMR should prove useful in the assignment of peaks in the spectrum of the parent xenobiotic such as in the identification of hernandulcin (16). The accurate assignment of a spectrum is often a prerequisite To the determination of the conjugate by NMR. 2-D NK was used in conjunction with 13c enrichment in a study of glycine metabolism in tobacco suspension cells (17). 

The excessive endogenous oxalate formation appears to be due to a metabolic change in glycine metabolism. Thus, Scowen et al. (S8) found that the administration of labeled glycine to such patients is followed by a prompt and considerable incorporation of the isotope into the urinary oxalate. The excessive glycine incorporation into urinary oxalate was confirmed recently in a patient with primary hyperoxaluria by Elder and Wyngaarden (El), who found, on the contrary, a normal incorporation in another patient having only inconstant hyperoxaluria. 

N-Methylation yields the monomethyl derivative sarcosine and also dimethylglycine, compounds that may function as osmoprotectants (Box 20-C). Many bacteria produce sarcosine oxidase, a fla-voprotein that oxidizes its substrate back to glycine and formaldehyde, which can react with tetrahydro-folate. The formation of porphobilinogen and the various pyrrole pigments derived from it and the synthesis of the purine ring (Chapter 25) represent two other major routes for glycine metabolism. 

A second condition, in which pathophysiology is primarily manifested in the brain, is nonketotic hyperglycinemia (NKH), a disorder of glycine metabolism. As mentioned above, the glycine cleavage complex resides in cells of the liver and brain only. While the liver is unaffected in this condition, increased amounts of glycine in... 

Glycine cleavage system an enzyme system accounting for a major proportion of glycine metabolism in vertebrate liver. It is composed of 4 proteins 1. P-protein, which contains pyridoxal phosphate, 2. H-protein, which acts as a carrier and contains lipoic acid, 3. L-protein (lipoamide dehydrogenase) and 4. T-protein, a transferase dependent on tetrahydrofolate. The following reactions occur ... 

In the serine-glycine metabolism, two disorders are discussed 3-phos-phoglycerate dehydrogenase deficiency, a synthesis defect and nonketotic hyperglycinemia, a catabolic defect. 

It was proposed by Shemin and Russell ( 9) that 5-AL not only gave rise to porphyrins but could be oxidized back to succinic acid. This would provide an alternate path for glycine oxidation. It is difficult to obtain a quantitative idea of the amount of 5-AL that is decomposed via this cycle. Experiments from Neuberger s laboratory (391) suggested that perhaps 30 % of the 5-AL formed may undergo oxidation. The complex relation of glycine metabolism and porphyrin synthesis has recently been carefully analyzed by Neuberger (55). 

Shafai, T., Sweetman, L., Weyler, W., Goodman, S.I., Fennessey, P.V. and Nyhan, W.L. (1978), Propionic acidemia with severe hyperammonemia and defective glycine metabolism. /. Pediatr., 92,84. 

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