Department of Animal Science, Texas A&M University, College Station, TX 77843, USA.
Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77843, USA.
Exp Biol Med (Maywood). 2023 Jul;248(14):1206-1220. doi: 10.1177/15353702231181360. Epub 2023 Aug 25.
Glycine from sow's milk only meets 20% of the requirement of suckling piglets. However, how glycine is synthesized endogenously in neonates is not known. This study determined glycine synthesis from 4-hydroxyproline (an abundant amino acid in milk and neonatal blood) in tissues of sow-reared piglets with normal birth weights. Piglets were euthanized at 0, 7, 14 and 21 days of age, and their tissues were used to determine glycine synthesis from 0 to 5 mM 4-hydroxyproline, activities and mRNA expression of key glycine-synthetic enzymes, and their cell-specific localization. Activities of 4-hydroxyproline oxidase (OH-POX), proline oxidase (POX), serine hydroxymethyltransferase (SHMT), threonine dehydrogenase (TDH), alanine:glyoxylate transaminase (AGT), and 4-hydroxy-2-oxoglutarate aldolase (HOA) occurred in the kidneys and liver from all age groups of piglets, and in the pancreas of 7- to 21-day-old piglets. Activities of OH-POX and HOA were absent from the small intestine of newborn pigs but present in the small intestine of 7- to 21-day-old piglets and in the skeletal muscle of 14- to 21-day-old piglets. Between days 0 and 21 of age, the enzymatic activities of OH-POX, AGT, and HOA decreased in the liver and kidneys but increased in the pancreas and small intestine with age. The mRNA levels of these three enzymes changed in a manner similar to their enzymatic activities. In contrast to OH-POX, AGT, and HOA, the enzymatic activities of POX, SHMT, and TDH were present in the kidneys, liver, and intestine of all age groups of piglets. Glycine was synthesized from 0.1 to 5 mM 4-hydroxyproline in the liver and kidney from 0- to 21-day-old piglets, as well as the pancreas, small intestine, and skeletal muscle from 14- to 21-day-old piglets in a concentration-dependent manner. Collectively, our findings indicate that 4-hydroxyproline is used for the synthesis of glycine in tissues of piglets to compensate for the deficiency of glycine in milk.
母猪奶中的甘氨酸仅能满足仔猪 20%的需求。然而，新生儿如何内源性合成甘氨酸尚不清楚。本研究旨在确定正常出生体重的母猪所产仔猪组织中从 4-羟脯氨酸（牛奶和新生儿血液中的一种丰富氨基酸）合成甘氨酸的情况。仔猪分别在 0、7、14 和 21 日龄时被安乐死，并用其组织测定 0 至 5mM 4-羟脯氨酸条件下的甘氨酸合成、关键甘氨酸合成酶的活性和 mRNA 表达及其细胞特异性定位。4-羟脯氨酸氧化酶（OH-POX）、脯氨酸氧化酶（POX）、丝氨酸羟甲基转移酶（SHMT）、苏氨酸脱氢酶（TDH）、丙氨酸：乙醛酸转氨酶（AGT）和 4-羟基-2-氧代戊二酸醛缩酶（HOA）的活性存在于所有年龄段仔猪的肾脏和肝脏中，并且存在于 7 至 21 日龄仔猪的胰腺中。新生仔猪小肠中不存在 OH-POX 和 HOA 的活性，但存在于 7 至 21 日龄仔猪的小肠和 14 至 21 日龄仔猪的骨骼肌中。0 至 21 日龄时，OH-POX、AGT 和 HOA 的酶活性在肝脏和肾脏中随年龄的增长而降低，而在胰腺和小肠中则增加。这些酶的 mRNA 水平的变化与其酶活性相似。与 OH-POX、AGT 和 HOA 不同，POX、SHMT 和 TDH 的酶活性存在于所有年龄段仔猪的肾脏、肝脏和肠道中。0 至 21 日龄仔猪的肝脏和肾脏以及 14 至 21 日龄仔猪的胰腺、小肠和骨骼肌均能以浓度依赖的方式从 0.1 至 5mM 4-羟脯氨酸合成甘氨酸。总之，我们的研究结果表明，4-羟脯氨酸可用于仔猪组织中甘氨酸的合成，以弥补牛奶中甘氨酸的不足。
