Lee T C, Qian C G, Snyder F
Medical Sciences Division, Oak Ridge Associated Universities, Tennessee 37831-0117.
Arch Biochem Biophys. 1991 May 1;286(2):498-503. doi: 10.1016/0003-9861(91)90071-p.
The alk-1-enyl bond in plasmenylethanolamine is formed from plasmanylethanolamine by the action of a microsomal cytochrome b5-dependent desaturase. However, the origin of the alk-1-enyl linkage in plasmenylcholine, a significant subclass of phospholipids in heart tissues of certain animal species, is not yet known. We have used neonatal rat myocytes as a model to study the biosynthesis of plasmenylcholine in the present studies since they have a phospholipid composition and subclasses of 1,2-diradyl-sn-glycero-3-phosphocholine (-GPC) similar to those of neonatal rat hearts. When equal concentrations of [3H]hexadecyllyso-GPC or [3H]hexadecyllyso-sn-glycero-3-phosphoethanolamine (-GPE) are incubated under identical conditions with myocytes for 4, 12, and 24 h, the rate of plasmenylcholine formation is faster from [3H]hexadecyllyso-GPE than from [3H]hexadecyllyso-GPC. Also, when [3H]alkyllyso-GPC and alkyllyso-[N-methyl-14C]GPC are incubated with rat myocytes for various times up to 24 h, the 3H/14C ratio in the diacyl-GPC plus alkylacyl-GPC fraction and alkyllyso-GPC remains relatively constant (3H/14C = 2.7), whereas the 3H/14C of plasmenylcholine increases from 0.3 at 2 h to 1.7 after 24 h. Finally, when the rat myocytes are prelabeled with [3H]alkyllyso-GPE for 4 h and then reincubated with either [14C]choline or [14C]methionine for 1 or 3 h, both [14C]choline and [14C]methionine are incorporated into plasmenylcholine, except the 14C/3H is much higher (5- to 15-fold) in the [14C]choline-labeled plasmenylcholine than in the [14C]methionine-labeled plasmenylcholine. Collectively, our data show plasmenylcholine is not directly derived from plasmanylcholine or lysoplasmanylcholine, but instead is formed from plasmenylethanolamine via some type of hydrolytic exchange mechanism, and the contribution of plasmenylethanolamine through methylation to the synthesis of plasmenylcholine is of limited capacity.
缩醛磷脂酰乙醇胺中的1-烯基键是由微粒体细胞色素b5依赖性去饱和酶作用于缩醛磷脂酰乙醇胺形成的。然而，在某些动物物种心脏组织中作为重要磷脂亚类的缩醛磷脂酰胆碱中1-烯基连接的起源尚不清楚。在本研究中，我们使用新生大鼠心肌细胞作为模型来研究缩醛磷脂酰胆碱的生物合成，因为它们的磷脂组成和1,2-二酰基-sn-甘油-3-磷酸胆碱（-GPC）亚类与新生大鼠心脏相似。当在相同条件下将等浓度的[3H]十六烷基溶血-GPC或[3H]十六烷基溶血-sn-甘油-3-磷酸乙醇胺（-GPE）与心肌细胞孵育4、12和24小时时，[3H]十六烷基溶血-GPE形成缩醛磷脂酰胆碱的速率比[3H]十六烷基溶血-GPC快。此外，当将[3H]烷基溶血-GPC和烷基溶血-[N-甲基-14C]GPC与大鼠心肌细胞孵育长达24小时的不同时间时，二酰基-GPC加烷基酰基-GPC部分和烷基溶血-GPC中的3H/14C比值保持相对恒定（3H/14C = 2.7），而缩醛磷脂酰胆碱的3H/14C从2小时时的0.3增加到24小时后的1.7。最后，当大鼠心肌细胞用[3H]烷基溶血-GPE预标记4小时，然后再与[14C]胆碱或[14C]甲硫氨酸孵育1或3小时时，[14C]胆碱和[14C]甲硫氨酸都掺入到缩醛磷脂酰胆碱中，只是[14C]胆碱标记的缩醛磷脂酰胆碱中的14C/3H比[14C]甲硫氨酸标记的缩醛磷脂酰胆碱中的高得多（5至15倍）。总体而言，我们的数据表明缩醛磷脂酰胆碱不是直接来源于缩醛磷脂酰胆碱或溶血缩醛磷脂酰胆碱，而是通过某种水解交换机制由缩醛磷脂酰乙醇胺形成，并且缩醛磷脂酰乙醇胺通过甲基化对缩醛磷脂酰胆碱合成的贡献能力有限。
