Shiao Y J, Vance J E
Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, Canada.
Biochem J. 1995 Sep 1;310 ( Pt 2)(Pt 2):673-9. doi: 10.1042/bj3100673.
Evidence is presented for the operation of an ethanolamine-phosphatidylethanolamine (PtdEtn) cycle in Chinese hamster ovary cells. PtdEtn was labelled with [3H]ethanolamine and radioactivity was chased by incubation with 1 mM unlabelled ethanolamine. Radioactivity in [3H]PtdEtn gradually declined over a 23 h time period. In contrast, when the cells were incubated in medium lacking unlabelled ethanolamine, radioactivity in PtdEtn remained constant for at least 23 h. These observations suggest that the ethanolamine moiety is continuously released from PtdEtn and recycled back into PtdEtn. In cells incubated without unlabelled ethanolamine, labelled ethanolamine released from PtdEtn is re-incorporated into PtdEtn without significant dilution. In contrast, in cells incubated with unlabelled ethanolamine the specific radioactivity of the intracellular ethanolamine pool decreases as a result of dilution by the exogenous ethanolamine, hence radioactivity in PtdEtn gradually declines. Similar results were obtained for confluent and non-confluent cells. Our data also demonstrate that when PtdEtn is derived from phosphatidylserine decarboxylation, the ethanolamine cycle operates only in actively dividing, and not in confluent, cells, implying that PtdEtn derived from different biosynthetic origins [i.e. from decarboxylation of phosphatidylserine or from ethanolamine (most likely via the CDP-ethanolamine pathway)] is metabolized differently.
有证据表明中国仓鼠卵巢细胞中存在乙醇胺 - 磷脂酰乙醇胺（PtdEtn）循环。用[³H]乙醇胺标记PtdEtn，并通过与1 mM未标记的乙醇胺孵育来追踪放射性。[³H]PtdEtn中的放射性在23小时内逐渐下降。相反，当细胞在缺乏未标记乙醇胺的培养基中孵育时，PtdEtn中的放射性至少23小时保持恒定。这些观察结果表明，乙醇胺部分不断从PtdEtn中释放出来，并循环回到PtdEtn中。在没有未标记乙醇胺孵育的细胞中，从PtdEtn释放的标记乙醇胺在没有明显稀释的情况下重新掺入PtdEtn中。相反，在与未标记乙醇胺孵育的细胞中，由于外源乙醇胺的稀释，细胞内乙醇胺池的比放射性降低，因此PtdEtn中的放射性逐渐下降。汇合细胞和未汇合细胞得到了类似的结果。我们的数据还表明，当PtdEtn源自磷脂酰丝氨酸脱羧时，乙醇胺循环仅在活跃分裂的细胞中起作用，而在汇合细胞中不起作用，这意味着源自不同生物合成来源[即源自磷脂酰丝氨酸的脱羧或源自乙醇胺（最可能通过CDP - 乙醇胺途径）]的PtdEtn代谢方式不同。
