高半胱氨酸 Homocysteine
（重定向自Homocysteinemia）
![](/Images/godic/202501/18/L-Homocysteine-3D-balls4545.png")
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高半胱氨酸（英语：Homocysteine，或称为同型半胱氨酸或同半胱氨酸）是氨基酸半胱氨酸的异种，在旁链部份硫醇基（-SH）前包含一个额外的亚甲基（-CH2-）。
Homocysteinemia
中文百科
英语百科
Homocysteine 高半胱氨酸
（重定向自Homocysteinemia）
![Two of homocysteine's main biochemical roles. (Homocysteine is seen in the left middle of the image.) It can be synthesized from methionine and then converted back to methionine via the SAM cycle or used to create cysteine and alpha-ketobutyrate.](/Images/godic/202501/18/Met_pathway4545.gif")
![MTHFR metabolism: folate cycle, methionine cycle, trans-sulfuration and hyperhomocysteinemia. 5-MTHF: 5-methyltetrahydrofolate; 5,10-methyltetrahydrofolate; BAX: Bcl-2-associated X protein; BHMT: betaine-homocysteine S-methyltransferase; CBS: cystathionine beta synthase; CGL: cystathionine gamma-lyase; DHF: dihydrofolate (vitamin B9); DMG: dimethylglycine; dTMP: thymidine monophosphate; dUMP: deoxyuridine monophosphate; FAD+ flavine adenine dicucleotide; FTHF: 10-formyltetrahydrofolate; MS: methionine synthase; MTHFR: mehtylenetetrahydrofolate reductase; SAH: S-adenosyl-L-homocysteine; SAME: S-adenosyl-L-methionine; THF: tetrahydrofolate.](/Images/godic/202501/18/MTHFR_metabolism.svg4545.png")
![Total plasma homocysteine](/Images/godic/202501/18/Plasma_tHcy.svg4546.png")
Homocysteine /ˌhoʊmoʊˈsɪstiːn/ is a non-protein α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH2-). It is biosynthesized from methionine by the removal of its terminal C methyl group. Homocysteine can be recycled into methionine or converted into cysteine with the aid of certain B-vitamins.