If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → Glycine Biosynthesis|
Pathway Summary from MetaCyc:
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
This single reaction pathway, catalyzed by serine hydroxymethyltransferase, is the major pathway for biosynthesis of glycine in Escherichia coli K-12, and the main source for one carbon units, which are stored in the form of 5,10-methylenetetrahydropteroyl mono-L-glutamate.
In Saccharomyces cerevisiae, mitochondrial and cytoplasmic serine hydroxymethyltransferase (SHMT) isozymes are encoded by distinct nuclear genes (SHM1 and SHM2). As in Escherichia coli, SHMT is the major provider of not only glycine, but also of one-carbon units [Kastanos97].
When yeast was grown on L-serine as the primary one-carbon source, the cytoplasmic isozyme was the main provider of glycine and one-carbon groups for purine synthesis. When grown on glycine, the mitochondrial SHMT was the predominant isozyme catalyzing the synthesis of serine from glycine and one-carbon units. However, when both serine and glycine were present, the mitochondrial SHMT made a significant contribution of one-carbon units, but not glycine, for purine synthesis [Kastanos97].
Superpathways: superpathway of serine and glycine biosynthesis I
Variants: glycine biosynthesis II
Pathway Evidence Glyph:
Created in MetaCyc 08-Jul-1994 by Riley M , Marine Biological Laboratory
Revised in MetaCyc 07-Jan-2008 by Caspi R , SRI International
Imported from MetaCyc 08-Aug-2014 by Subhraveti P , SRI International
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
Jabrin03: Jabrin S, Ravanel S, Gambonnet B, Douce R, Rebeille F (2003). "One-carbon metabolism in plants. Regulation of tetrahydrofolate synthesis during germination and seedling development." Plant Physiol 131(3);1431-9. PMID: 12644692
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