The proteinogenic amino acid glycine can biosynthesized via several different pathways. The main pathway in most organisms is the production of glycine from L-serine via EC 2.1.2.1, glycine hydroxymethyltransferase. Eukaryotic organisms have both a cytosolic enzyme (SHMT2) and a mitochondrial enzyme (SHMT1) (see glycine biosynthesis I). The two isoforms were reported to work in opposite directions depending on the culture conditions.
In a third pathway glycine is formed from glyoxylate, a product of the glyoxylate cycle, by the enzyme EC 2.6.1.44, alanine—glyoxylate transaminase (see glycine biosynthesis III).
And finally, glycine can also be formed from L-threonine by the action of EC 4.1.2.48, low-specificity L-threonine aldolase (see glycine biosynthesis IV).
Description adapted from https://pathway.yeastgenome.org/.