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:
This organism is in the expected taxonomic range for this pathway.
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
©2015 SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025-3493