Threonine and methionine biosynthesis

The biosynthesis of threonine and methionine in S. cerevisiae begins in a common three-step pathway that converts aspartate to homoserine. HOM3 and HOM2, which encode the enzymes responsible for the first and second steps of this pathway respectively, are regulated by Gcn4p under the general control of amino acid biosynthesis. Additionally, threonine represses HOM3 and competitively inhibits homoserine dehydrogenase (encoded by HOM6), lending that the flow of carbon into the common pathway is primarily regulated by threonine. The Hom3p, Hom2p, and Hom6p-catalyzed reactions yield homoserine, at which point the threonine and methionine pathways diverge. Phosphorylation of homoserine by homoserine kinase (encoded by THR1) directs homoserine towards the biosynthesis of threonine, whereas acetylation by homoserine O-transacetylase (encoded by MET2) commits homoserine to the biosynthesis of sulfur amino acids. Source: https://pathway.yeastgenome.org/

苏氏酵母中苏氨酸和蛋氨酸的生物合成过程始于一条将天冬氨酸转化为同型丝氨酸的共同三步途径。编码此途径第一步和第二步酶的HOM3和HOM2基因，在氨基酸生物合成的一般控制下，受Gcn4p的调控。此外，苏氨酸可抑制HOM3，并竞争性地抑制同型丝氨酸脱氢酶（由HOM6编码），表明碳流进入共同途径的主要调控机制为苏氨酸。由Hom3p、Hom2p和Hom6p催化的反应产生同型丝氨酸，此时苏氨酸和蛋氨酸途径分叉。同型丝氨酸激酶（由THR1编码）的磷酸化作用将同型丝氨酸导向苏氨酸的生物合成途径，而同型丝氨酸O-转乙酰酶（由MET2编码）的乙酰化作用则将同型丝氨酸固定于硫氨基酸的生物合成途径。来源：https://pathway.yeastgenome.org/