Robinson Jason L, McBreairty Laura E, Randell Edward W, Brunton Janet A, Bertolo Robert F
Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3X9.
Department of Laboratory Medicine, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3X9.
J Nutr Biochem. 2016 Sep;35:81-86. doi: 10.1016/j.jnutbio.2016.07.001. Epub 2016 Jul 9.
Methionine is required for protein synthesis and provides a methyl group for >50 critical transmethylation reactions including creatine and phosphatidylcholine synthesis as well as DNA and protein methylation. However, the availability of methionine depends on dietary sources as well as remethylation of demethylated methionine (i.e., homocysteine) by the dietary methyl donors folate and choline (via betaine). By restricting dietary methyl supply, we aimed to determine the extent that dietary methyl donors contribute to methionine availability for protein synthesis and transmethylation reactions in neonatal piglets. Piglets 4-8 days of age were fed a diet deficient (MD-) (n=8) or sufficient (MS+) (n=7) in folate, choline and betaine. After 5 days, dietary methionine was reduced to 80% of requirement in both groups to elicit a response. On day 8, animals were fed [(3)H-methyl]methionine for 6h to measure methionine partitioning into hepatic protein, phosphatidylcholine, creatine and DNA. MD- feeding reduced plasma choline, betaine and folate (P<.05) and increased homocysteine ~3-fold (P<.05). With MD- feeding, hepatic phosphatidylcholine synthesis was 60% higher (P<.05) at the expense of creatine synthesis, which was 30% lower during MD- feeding (P<.05); protein synthesis as well as DNA and protein methylation were unchanged. In the liver, ~30% of dietary label was traced to phosphatidylcholine and creatine together, with ~50% traced to methylation of proteins and ~20% incorporated in synthesized protein. Dietary methyl donors are integral to neonatal methionine requirements and can affect methionine availability for transmethylation pathways.
蛋氨酸是蛋白质合成所必需的，并为50多种关键的转甲基反应提供甲基，包括肌酸和磷脂酰胆碱的合成以及DNA和蛋白质的甲基化。然而，蛋氨酸的可用性取决于饮食来源以及通过饮食中的甲基供体叶酸和胆碱（通过甜菜碱）对去甲基化蛋氨酸（即同型半胱氨酸）的再甲基化。通过限制饮食中的甲基供应，我们旨在确定饮食中的甲基供体在多大程度上有助于新生仔猪蛋白质合成和转甲基反应中蛋氨酸的可用性。给4-8日龄的仔猪喂食叶酸、胆碱和甜菜碱缺乏（MD-）（n=8）或充足（MS+）（n=7）的日粮。5天后，两组日粮蛋氨酸均降至需求量的80%以引发反应。在第8天，给动物喂食[(3)H-甲基]蛋氨酸6小时，以测量蛋氨酸在肝脏蛋白质、磷脂酰胆碱、肌酸和DNA中的分配情况。MD-喂养降低了血浆胆碱、甜菜碱和叶酸（P<0.05），并使同型半胱氨酸增加了约3倍（P<0.05）。MD-喂养时，肝脏磷脂酰胆碱合成增加60%（P<0.05），代价是肌酸合成，MD-喂养期间肌酸合成降低30%（P<0.05）；蛋白质合成以及DNA和蛋白质甲基化未发生变化。在肝脏中，约30%的日粮标记物一起追踪到磷脂酰胆碱和肌酸，约50%追踪到蛋白质甲基化，约20%掺入合成蛋白质中。饮食中的甲基供体是新生仔猪蛋氨酸需求所必需的，并且可以影响转甲基途径中蛋氨酸的可用性。
