Glycine hydroxymethyltransferase; Catalyzes the reversible interconversion of serine and glycine with tetrahydrofolate (THF) serving as the one-carbon carrier. This reaction serves as the major source of one-carbon groups required for the biosynthesis of purines, thymidylate, methionine, and other important biomolecules. Also exhibits THF-independent aldolase activity toward beta-hydroxyamino acids, producing glycine and aldehydes, via a retro-aldol mechanism.

Methionine synthase (B12-dependent); Catalyzes the transfer of a methyl group from methyl- cobalamin to homocysteine, yielding enzyme-bound cob(I)alamin and methionine. Subsequently, remethylates the cofactor using methyltetrahydrofolate.

Homoserine dehydrogenase.

Tryptophan synthase, beta chain; The beta subunit is responsible for the synthesis of L- tryptophan from indole and L-serine.

Threonine synthase.

Homoserine O-acetyltransferase; Transfers a succinyl group from succinyl-CoA to L-homoserine, forming succinyl-L-homoserine.

Serine O-acetyltransferase.

Threonine dehydratase; Catalyzes the anaerobic formation of alpha-ketobutyrate and ammonia from threonine in a two-step reaction. The first step involved a dehydration of threonine and a production of enamine intermediates (aminocrotonate), which tautomerizes to its imine form (iminobutyrate). Both intermediates are unstable and short-lived. The second step is the nonenzymatic hydrolysis of the enamine/imine intermediates to form 2- ketobutyrate and free ammonia. In the low water environment of the cell, the second step is accelerated by RidA.

Branched-chain amino acid aminotransferase; Acts on leucine, isoleucine and valine. Belongs to the class-IV pyridoxal-phosphate-dependent aminotransferase family.