Wu G, Flynn N E, Yan W, Barstow D G
Department of Animal Science, Texas A&M University, College Station 77843-2471.
Biochem J. 1995 Mar 15;306 ( Pt 3)(Pt 3):717-21. doi: 10.1042/bj3060717.
This study was designed to determine whether pyrroline-5-carboxylate (P-5-C) synthase is deficient in chick enterocytes therefore resulting in the lack of synthesis of ornithine and citrulline from glutamine. Post-weaning pig enterocytes, which are known to contain P-5-C synthase and to synthesize both ornithine and citrulline from glutamine, were used as positive controls. Enterocytes were incubated at 37 degrees C for 0-30 min in the presence of 2 mM [U-14C]glutamine or 2 mM ornithine plus 2 mM NH4Cl. In chick enterocytes, glutamine was metabolized to NH3, CO2, glutamate, alanine and aspartate, but not to ornithine, citrulline, arginine or proline. Likewise, there was no formation of citrulline, arginine, alanine or aspartate from ornithine in chick enterocytes. Furthermore, the rate of conversion of ornithine into proline in chick enterocytes was only about 4% of that in cells from pigs. To elucidate the reason for the inability of chick enterocytes to synthesize ornithine and citrulline from glutamine, the activities of the enzymes involved were measured. No activity of P-5-C synthase or ornithine carbamoyltransferase was found in chick enterocytes, in contrast with cells from post-weaning pigs. It was also demonstrated that the activity of ornithine aminotransferase in chick enterocytes was only 3% of that in cells from pigs. Thus the present findings elucidate the biochemical reason for the lack of endogenous synthesis of ornithine and citrulline in chicks. Our results also explain previous observations that ornithine cannot replace arginine or proline in the diet of chicks. We suggest that the absence of P-5-C synthase and ornithine carbamoyltransferase in enterocytes is the metabolic basis for the nutritional requirement of arginine in the chick.
本研究旨在确定雏鸡肠细胞中吡咯啉 - 5 - 羧酸（P - 5 - C）合酶是否缺乏，从而导致无法从谷氨酰胺合成鸟氨酸和瓜氨酸。已知断奶后仔猪肠细胞含有P - 5 - C合酶并能从谷氨酰胺合成鸟氨酸和瓜氨酸，将其用作阳性对照。肠细胞在37℃下于2 mM [U - 14C]谷氨酰胺或2 mM鸟氨酸加2 mM氯化铵存在的条件下孵育0 - 30分钟。在雏鸡肠细胞中，谷氨酰胺代谢为NH3、CO2、谷氨酸、丙氨酸和天冬氨酸，但不代谢为鸟氨酸、瓜氨酸、精氨酸或脯氨酸。同样，雏鸡肠细胞中鸟氨酸也不会生成瓜氨酸、精氨酸、丙氨酸或天冬氨酸。此外，雏鸡肠细胞中鸟氨酸转化为脯氨酸的速率仅约为猪细胞中的4%。为阐明雏鸡肠细胞无法从谷氨酰胺合成鸟氨酸和瓜氨酸的原因，对相关酶的活性进行了测定。与断奶后仔猪的细胞不同，在雏鸡肠细胞中未发现P - 5 - C合酶或鸟氨酸氨甲酰转移酶的活性。还证明雏鸡肠细胞中鸟氨酸转氨酶的活性仅为猪细胞中的3%。因此，本研究结果阐明了雏鸡内源性鸟氨酸和瓜氨酸合成缺乏的生化原因。我们的结果也解释了先前的观察结果，即鸟氨酸不能替代雏鸡日粮中的精氨酸或脯氨酸。我们认为肠细胞中缺乏P - 5 - C合酶和鸟氨酸氨甲酰转移酶是雏鸡对精氨酸营养需求的代谢基础。
