Le Floc'h N, Thibault J N, Sève B
Station de Recherches Porcines, INRA 35590 Saint Gilles, France.
Br J Nutr. 1997 Apr;77(4):593-603. doi: 10.1079/bjn19970059.
Two experiments were designed to determine the tissue distribution of threonine oxidation through the threonine dehydrogenase (EC 1.1.1.103) pathway in pigs. The first experiment was conducted on eleven Piétrain x Large White piglets. The piglets were slaughtered at 5, 12 or 20 kg after 1 h of infusion with L-[U-14C]threonine (55 kBq/kg) mixed with unlabelled threonine (100 mg/kg). In the second experiment, four Piétrain x Large White and four large White piglets (10 kg body weight) were infused with L-[1-13C]threonine (50 mg/kg) mixed with 50 mg/kg unlabelled threonine for 1 h, then killed for tissue sampling. In the two experiments, threonine dehydrogenase specific activity and threonine and glycine specific radioactivities and enrichments were measured in several tissues and in plasma. The higher level of labelling of threonine in the pancreas than in the liver suggested either a lower protein degradation rate or a faster rate of threonine transport in the liver than in the pancreas. Threonine dehydrogenase activity was found only in the liver and the pancreas. Whereas liver and pancreas threonine dehydrogenase specific activities were similar, glycine specific radioactivity and enrichment were 12- to 14-fold higher in the pancreas than in the liver. This is probably the consequence of a higher production rate of glycine from sources other than threonine (protein degradation, de novo synthesis from serine) in the liver than in the pancreas. Our results showed that Large White pigs could oxidize more threonine than Piétrain x Large White pigs. This could be related to the difference in growth performance and dietary N efficiency for protein deposition between these two genotypes.
设计了两个实验来确定猪体内通过苏氨酸脱氢酶（EC 1.1.1.103）途径进行的苏氨酸氧化的组织分布。第一个实验选用了11头皮特兰×大白仔猪。仔猪在输注含有未标记苏氨酸（100毫克/千克）的L-[U-¹⁴C]苏氨酸（55千贝克勒尔/千克）1小时后，分别在体重达5、12或20千克时屠宰。在第二个实验中，对4头皮特兰×大白仔猪和4头大白仔猪（体重10千克）输注含有50毫克/千克未标记苏氨酸的L-[¹-¹³C]苏氨酸（50毫克/千克）1小时，然后宰杀进行组织采样。在这两个实验中，测定了几个组织和血浆中苏氨酸脱氢酶的比活性以及苏氨酸和甘氨酸的比放射性和富集情况。胰腺中苏氨酸的标记水平高于肝脏，这表明肝脏中的蛋白质降解速率较低，或者肝脏中苏氨酸的转运速率比胰腺中慢。仅在肝脏和胰腺中发现了苏氨酸脱氢酶活性。虽然肝脏和胰腺中苏氨酸脱氢酶的比活性相似，但胰腺中甘氨酸的比放射性和富集程度比肝脏中高12至14倍。这可能是因为肝脏中从苏氨酸以外的来源（蛋白质降解、由丝氨酸从头合成）产生甘氨酸的速率高于胰腺。我们的结果表明，大白猪比皮特兰×大白猪能氧化更多的苏氨酸。这可能与这两种基因型在生长性能和蛋白质沉积的日粮氮效率方面的差异有关。
