McBreairty Laura E, Robinson Jason L, Harding Scott V, Randell Edward W, Brunton Janet A, Bertolo Robert F
Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada.
Diabetes and Nutritional Sciences Division, King's College London, London, SE1 9NH, United Kingdom.
Eur J Nutr. 2016 Dec;55(8):2423-2430. doi: 10.1007/s00394-015-1049-0. Epub 2015 Sep 29.
Both folate and betaine (synthesized from choline) are nutrients used to methylate homocysteine to reform the amino acid methionine following donation of its methyl group; however, it is unclear whether both remethylation pathways are of equal importance during the neonatal period when remethylation rates are high. Methionine is an indispensable amino acid that is in high demand in neonates not only for protein synthesis, but is also particularly important for transmethylation reactions, such as creatine and phosphatidylcholine synthesis. The objective of this study was to determine whether supplementation with folate, betaine, or a combination of both can equally re-synthesize methionine for protein synthesis when dietary methionine is limiting.
Piglets were fed a low methionine diet devoid of folate, choline, and betaine, and on day 6, piglets were supplemented with either folate, betaine, or folate + betaine (n = 6 per treatment) until day 10. [1-C]-phenylalanine oxidation was measured as an indicator of methionine availability for protein synthesis both before and after 2 days of supplementation.
Prior to supplementation, piglets had lower concentrations of plasma folate, betaine, and choline compared to baseline with no change in homocysteine. Post-supplementation, phenylalanine oxidation levels were 20-46 % lower with any methyl donor supplementation (P = 0.006) with no difference among different supplementation groups. Furthermore, both methyl donors led to similarly lower concentrations of homocysteine following supplementation (P < 0.05).
These data demonstrate an equal capacity for betaine and folate to remethylate methionine for protein synthesis, as indicated by lower phenylalanine oxidation.
叶酸和甜菜碱（由胆碱合成）都是用于将同型半胱氨酸甲基化以在其甲基供体后重新形成蛋氨酸的营养素；然而，在新生儿期甲基化率较高时，这两种再甲基化途径是否同等重要尚不清楚。蛋氨酸是一种必需氨基酸，新生儿不仅对其蛋白质合成有高需求，而且对转甲基反应（如肌酸和磷脂酰胆碱合成）也特别重要。本研究的目的是确定当膳食蛋氨酸有限时，补充叶酸、甜菜碱或两者的组合是否能同等地重新合成蛋氨酸用于蛋白质合成。
给仔猪喂食不含叶酸、胆碱和甜菜碱的低蛋氨酸日粮，在第6天，给仔猪补充叶酸、甜菜碱或叶酸 + 甜菜碱（每组n = 6），直至第10天。在补充2天前后，测量[1-C]-苯丙氨酸氧化作为蛋白质合成中蛋氨酸可用性的指标。
补充前，与基线相比，仔猪血浆叶酸、甜菜碱和胆碱浓度较低，同型半胱氨酸无变化。补充后，任何甲基供体补充组的苯丙氨酸氧化水平均降低20 - 46%（P = 0.006），不同补充组之间无差异。此外，两种甲基供体补充后均导致同型半胱氨酸浓度同样降低（P < 0.05）。
这些数据表明，甜菜碱和叶酸在重新甲基化蛋氨酸用于蛋白质合成方面具有同等能力，这由较低的苯丙氨酸氧化所表明。
