Welsch F, Wenger W C, Stedman D B
Placenta. 1981 Jul-Sep;2(3):211-21. doi: 10.1016/s0143-4004(81)80004-5.
Microsomes from human, mouse and rat placenta were found to contain enzymatic activity which methylates the phospholipids phosphatidylethanolamine (PE), phosphatidyl-N-monomethylethanolamine (PMME) and phosphatidyl-N,N-dimethylethanolamine (PDME) to form phosphatidylcholine (PCh) with 3H-methyl-S-adenosyl-l-methionine as the methyl donor. The three labelled reaction products were isolated by solvent extraction and separated on thin-layer chromatography (TLC) plates. The endogenous methyltransferase activity was low, indicating that the methylation pathway is quantitatively not important for the synthesis of free choline to meet the fetal needs. The distribution of 3H-methyl among PMME, PDME and PCh revealed fairly even labelling of all products when analysed by TLC. Addition of authentic PE, PMME and PDME to a level of approximately 2.5 mM stimulated the incorporation of 3H-methyl into the total lipid-soluble fraction with all three substrates, but was most pronounced with PMME. Present observations suggest that all three methylation steps were catalysed by one enzyme with a pH optimum of 9.0 in a reaction that does not require Mg++.
研究发现，人、小鼠和大鼠胎盘的微粒体含有一种酶活性，该活性可利用3H-甲基-S-腺苷-L-甲硫氨酸作为甲基供体，将磷脂酰乙醇胺（PE）、磷脂酰-N-单甲基乙醇胺（PMME）和磷脂酰-N，N-二甲基乙醇胺（PDME）甲基化，形成磷脂酰胆碱（PCh）。通过溶剂萃取分离出三种标记的反应产物，并在薄层色谱（TLC）板上进行分离。内源性甲基转移酶活性较低，这表明甲基化途径在满足胎儿需求的游离胆碱合成中，在数量上并不重要。当通过TLC分析时，3H-甲基在PMME、PDME和PCh中的分布显示所有产物的标记相当均匀。添加约2.5 mM水平的纯品PE、PMME和PDME，可刺激所有三种底物将3H-甲基掺入总脂溶性部分，但对PMME最为明显。目前的观察结果表明，所有三个甲基化步骤均由一种酶催化，该酶在不需要Mg++的反应中，最适pH为9.0。
