Pajares M A, Villalba M, Mato J M
Biochem J. 1986 Aug 1;237(3):699-705. doi: 10.1042/bj2370699.
Phospholipid methyltransferase, the enzyme that converts phosphatidylethanolamine into phosphatidylcholine with S-adenosyl-L-methionine as the methyl donor, was purified to apparent homogeneity from rat liver microsomal fraction. When analysed by SDS/polyacrylamide-gel electrophoresis only one protein, with molecular mass about 50 kDa, is detected. This protein could be phosphorylated at a single site by incubation with [alpha-32P]ATP and the catalytic subunit of cyclic AMP-dependent protein kinase. A less-purified preparation of the enzyme is mainly composed of two proteins, with molecular masses about 50 kDa and 25 kDa, the 50 kDa form being phosphorylated at the same site as the homogeneous enzyme. After purification of both proteins by electro-elution, the 25 kDa protein forms a dimer and migrates on SDS/polyacrylamide-gel electrophoresis with molecular mass about 50 kDa. Peptide maps of purified 25 kDa and 50 kDa proteins are identical, indicating that both proteins are formed by the same polypeptide chain(s). It is concluded that rat liver phospholipid methyltransferase can exist in two forms, as a monomer of 25 kDa and as a dimer of 50 kDa. The dimer can be phosphorylated by cyclic AMP-dependent protein kinase.
磷脂甲基转移酶是一种以S-腺苷-L-甲硫氨酸作为甲基供体，将磷脂酰乙醇胺转化为磷脂酰胆碱的酶，已从大鼠肝脏微粒体部分纯化至表观均一。通过SDS/聚丙烯酰胺凝胶电泳分析时，仅检测到一种分子量约为50 kDa的蛋白质。该蛋白质与[α-32P]ATP和环磷酸腺苷依赖性蛋白激酶的催化亚基一起孵育时，可在单个位点被磷酸化。酶的一种纯化程度较低的制剂主要由两种蛋白质组成，分子量分别约为50 kDa和25 kDa，50 kDa形式的蛋白质在与均一酶相同的位点被磷酸化。通过电洗脱纯化这两种蛋白质后，25 kDa的蛋白质形成二聚体，并在SDS/聚丙烯酰胺凝胶电泳上以分子量约为50 kDa的形式迁移。纯化的25 kDa和50 kDa蛋白质的肽图相同，表明这两种蛋白质由相同的多肽链组成。得出的结论是，大鼠肝脏磷脂甲基转移酶可以以两种形式存在，即25 kDa的单体和50 kDa的二聚体。二聚体可被环磷酸腺苷依赖性蛋白激酶磷酸化。
