Serine - Serine has many important biological roles, including the biosynthesis of phosphopholipids and cysteine. Serine also contributes activated one-carbon units to the pool of tetrahydrofolate coenzymes. Serine can be made in a variety of ways, including the way shown here and Figure 21.24. Serine is catabolized by conversion to glycine or by action of serine-threonine dehydratase (Figure 21.25).

Glycine - Glycine also contributes to the one-carbon pool, to formation of glutathione, to purine nucleotides (see here), and to porphyrins (Figure 21.24). Glycine can be made as a cleavage product of threonine by threonine aldolase (see here). Glycine is catabolized via the mitochondrial glycine cleavage system to yield NH3, CO2, and 5,10-methylenetetrahydrofolate.

Threonine - Threonine is an essential amino acid in animals. Its synthesis is confined to plants and prokaryotes. Threonine can be cleaved by threonine aldolase to yield glycine and acetaldehyde (see here). Threonine is also acted on by serine-threonine dehydratase (Figure 21.25).

INTERNET LINK: Gly, Ser, Thr Metabolism