This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → Glycine Biosynthesis|
Some taxa known to possess this pathway include : Saccharomyces cerevisiae
Expected Taxonomic Range: Fungi
Saccharomyces cerevisiae can biosynthesize glycine via three different pathways. When the cells are grown with glucose as the carbon source, two alternative pathways operate. In one pathway L-threonine aldolase, encoded by GLY1, produces glycine from L-threonine (which is produced from the glycolytic intermediate oxaloacetate) (see glycine biosynthesis IV). In the other pathway glycine is formed from L-serine (a product of 3-phospho-D-glycerate, another glycolytic intermediate) via two serine hydroxymethyltransferases - a cytosolic enzyme (SHMT2) and a mitochondrial enzyme (SHMT1) (see glycine biosynthesis I). The two isoforms are reported to work in opposite directions, depending on the culture conditions [Kastanos97].
When the cells are grown with a non-fermentable carbon source, such as ethanol and acetate, glycine is produced from glyoxylate, a product of the glyoxylate cycle, by the enzyme alanine--glyoxylate aminotransferase 1 (see glycine biosynthesis III).
About This Pathway
It has been recognized since 1969 that many organisms possess an L-threonine aldolase that catalyzes the interconversion of L-threonine and glycine [Morris69]. The enzyme is widespread in nature and has been shown to exist in both eukaryotes and prokaryotes [Yamada70, Liu97c, Kataoka97, Kataoka97a, Liu98b, Liu98c, Joshi06]. In yeast the enzyme is important for the synthesis of cellular glycine [Monschau97]. In bacteria, despite the enzyme's wide distribution, its physiological significance is not certain.
Joshi06: Joshi V, Laubengayer KM, Schauer N, Fernie AR, Jander G (2006). "Two Arabidopsis threonine aldolases are nonredundant and compete with threonine deaminase for a common substrate pool." Plant Cell 18(12);3564-75. PMID: 17172352
Kastanos97: Kastanos EK, Woldman YY, Appling DR (1997). "Role of mitochondrial and cytoplasmic serine hydroxymethyltransferase isozymes in de novo purine synthesis in Saccharomyces cerevisiae." Biochemistry 36(48);14956-64. PMID: 9398220
Kataoka97: Kataoka M, Wada M, Nishi K, Yamada H, Shimizu S (1997). "Purification and characterization of L-allo-threonine aldolase from Aeromonas jandaei DK-39." FEMS Microbiol Lett 151(2);245-8. PMID: 9228760
Kataoka97a: Kataoka M, Ikemi M, Morikawa T, Miyoshi T, Nishi K, Wada M, Yamada H, Shimizu S (1997). "Isolation and characterization of D-threonine aldolase, a pyridoxal-5'-phosphate-dependent enzyme from Arthrobacter sp. DK-38." Eur J Biochem 248(2);385-93. PMID: 9346293
Liu97c: Liu JQ, Nagata S, Dairi T, Misono H, Shimizu S, Yamada H (1997). "The GLY1 gene of Saccharomyces cerevisiae encodes a low-specific L-threonine aldolase that catalyzes cleavage of L-allo-threonine and L-threonine to glycine--expression of the gene in Escherichia coli and purification and characterization of the enzyme." Eur J Biochem 245(2);289-93. PMID: 9151955
Liu98b: Liu JQ, Ito S, Dairi T, Itoh N, Kataoka M, Shimizu S, Yamada H (1998). "Gene cloning, nucleotide sequencing, and purification and characterization of the low-specificity L-threonine aldolase from Pseudomonas sp. strain NCIMB 10558." Appl Environ Microbiol 64(2);549-54. PMID: 9464392
Liu98c: Liu JQ, Dairi T, Itoh N, Kataoka M, Shimizu S, Yamada H (1998). "Gene cloning, biochemical characterization and physiological role of a thermostable low-specificity L-threonine aldolase from Escherichia coli." Eur J Biochem 1998;255(1);220-6. PMID: 9692922
Monschau97: Monschau N, Stahmann KP, Sahm H, McNeil JB, Bognar AL (1997). "Identification of Saccharomyces cerevisiae GLY1 as a threonine aldolase: a key enzyme in glycine biosynthesis." FEMS Microbiol Lett 150(1);55-60. PMID: 9163906
Contestabile01: Contestabile R, Paiardini A, Pascarella S, di Salvo ML, D'Aguanno S, Bossa F (2001). "l-Threonine aldolase, serine hydroxymethyltransferase and fungal alanine racemase. A subgroup of strictly related enzymes specialized for different functions." Eur J Biochem 268(24);6508-25. PMID: 11737206
Kim10a: Kim J, Kershner JP, Novikov Y, Shoemaker RK, Copley SD (2010). "Three serendipitous pathways in E. coli can bypass a block in pyridoxal-5'-phosphate synthesis." Mol Syst Biol 6;436. PMID: 21119630
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