菜豆胚乳中磷脂酰胆碱的合成：S-腺苷-L-蛋氨酸：乙醇胺 N-甲基转移酶的出现。
Phosphatidylcholine Synthesis in Castor Bean Endosperm : Occurrence of an S-Adenosyl-l-Methionine:Ethanolamine N-Methyltransferase.
机构信息
Department of Botany, Louisiana State University, Baton Rouge, Louisiana 70803-1705.
出版信息
Plant Physiol. 1992 Nov;100(3):1536-40. doi: 10.1104/pp.100.3.1536.
Methylethanolamine synthesis by S-adenosyl-l-methionine:ethanolamine N-methyltransferase from an extract of castor bean (Ricinus communis L. var Hale) endosperm was characterized. The apparent Michaelis-Menten constants of the enzyme for ethanolamine and S-adenosyl-l-methionine were estimated to be 6.7 and 1.4 mum, respectively, although the K(m) for ethanolamine is imprecise because of strong substrate inhibition. The pH optimum was 8.0, and a divalent cation was required for activity, with Mg(2+) giving the greatest stimulation at 5 mm. The enzyme was inhibited by calcium in the micromolar range and relatively high concentrations of ethanolamine (above about 7 mum). The activity was found in the 119,000g supernatant fraction and, therefore, appears to be cytoplasmic. The potential roles of S-adenosyl-l-methionine:ethanolamine N-methyltransferase in choline and phosphatidylcholine synthesis are discussed.
蓖麻油（Ricinus communis L. var Hale）胚乳提取物中的 S-腺苷-L-蛋氨酸：乙醇胺 N-甲基转移酶催化甲醇胺合成。尽管由于强烈的底物抑制作用，乙醇胺的 K(m)值不太精确，但该酶对乙醇胺和 S-腺苷-L-蛋氨酸的表观米氏常数估计分别为 6.7 和 1.4 μm。最适 pH 值为 8.0，需要二价阳离子才能发挥活性，5mm 时 Mg(2+)的刺激作用最大。该酶受钙的微摩尔范围和相对高浓度的乙醇胺（高于约 7μm）的抑制。该活性存在于 119,000g 上清液部分中，因此似乎是细胞质的。讨论了 S-腺苷-L-蛋氨酸：乙醇胺 N-甲基转移酶在胆碱和磷脂酰胆碱合成中的潜在作用。
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