Cystathionine gamma-synthase, PLP-dependent; Catalyzes the formation of L-cystathionine from O-succinyl-L- homoserine (OSHS) and L-cysteine, via a gamma-replacement reaction. In the absence of thiol, catalyzes gamma-elimination to form 2- oxobutanoate, succinate and ammonia.

Homoserine kinase; Catalyzes the ATP-dependent phosphorylation of L-homoserine to L-homoserine phosphate. Is also able to phosphorylate the hydroxy group on gamma-carbon of L-homoserine analogs when the functional group at the alpha-position is a carboxyl, an ester, or even a hydroxymethyl group. Neither L-threonine nor L-serine are substrates of the enzyme.

Aspartate-semialdehyde dehydrogenase, NAD(P)-binding; Catalyzes the NADPH-dependent formation of L-aspartate- semialdehyde (L-ASA) by the reductive dephosphorylation of L-aspartyl- 4-phosphate.

L-threonine synthase; Catalyzes the gamma-elimination of phosphate from L- phosphohomoserine and the beta-addition of water to produce L- threonine. To a lesser extent, is able to slowly catalyze the deamination of L-threonine into alpha-ketobutyrate and that of L-serine and 3-chloroalanine into pyruvate. Is also able to rapidly convert vinylglycine to threonine, which proves that the pyridoxal p-quinonoid of vinylglycine is an intermediate in the TS reaction.

Dihydrodipicolinate synthase; Catalyzes the condensation of (S)-aspartate-beta-semialdehyde [(S)-ASA] and pyruvate to 4-hydroxy-tetrahydrodipicolinate (HTPA). Belongs to the DapA family.

Homoserine O-transsuccinylase; Transfers a succinyl group from succinyl-CoA to L-homoserine, forming succinyl-L-homoserine. Utilizes a ping-pong kinetic mechanism in which the succinyl group of succinyl-CoA is initially transferred to the enzyme to form a succinyl-enzyme intermediate before subsequent transfer to homoserine to form the final product, O- succinylhomoserine. Cannot use acetyl-CoA. Belongs to the MetA family.

5,10-methylenetetrahydrofolate reductase; Methylenetetrahydrofolate reductase required to generate the methyl groups necessary for methionine synthetase to convert homocysteine to methionine.

Lysine-sensitive aspartokinase 3; Aspartokinase III, lysine sensitive; Protein involved in lysine biosynthetic process via diaminopimelate and homoserine biosynthetic process.

Transcriptional repressor, S-adenosylmethionine-binding; This regulatory protein, when combined with SAM (S- adenosylmethionine) represses the expression of the methionine regulon and of enzymes involved in SAM synthesis. It is also autoregulated.