This study tested the hypothesis that amino acids are oxidized at higher rates than glucose and palmitate for ATP production in tissues of largemouth bass (LMB, a carnivorous fish). Slices (10 to 50 mg) of liver, proximal intestine, kidney, and skeletal muscle isolated from LMB were incubated at 26 °C for 2 h in oxygenated Krebs–Henseleit bicarbonate buffer (pH 7.4, with 5 mM d-glucose) containing either d-[U-¹⁴C]glucose, 2 mM l-alanine plus l-[U-¹⁴C]alanine, 2 mM l-aspartate plus l-[U-¹⁴C]aspartate, 2 mM l-glutamate plus l-[U-¹⁴C]glutamate, 2 mM l-glutamine plus l-[U-¹⁴C]glutamine, 2 mM l-leucine plus l-[U-¹⁴C]leucine, or 2 mM palmitate plus [U-¹⁴C]palmitate. In parallel experiments, tissues were incubated with a [U-¹⁴C]-labeled tracer and a mixture of unlabeled substrates [alanine, aspartate, glutamate, glutamine, leucine, and palmitate (2 mM each) plus 5 mM glucose]. ¹⁴CO₂ was collected to calculate the rates of substrate oxidation. In separate experiments, O₂ consumption by each tissue was measured in the presence of individual or a mixture of substrates. The activities of key metabolic enzymes were also measured. Results indicated that the liver and skeletal muscle had a limited ability to oxidize glucose and palmitate to CO₂ for ATP production in the presence of individual or a mixture of substrates due to low activities of carnitine palmitoyltransferase-I, hexokinase and pyruvate dehydrogenase. In the presence of individual substrates, each amino acid was actively oxidized by all the tissues. In the presence of a mixture of substrates, glutamine and glutamate were the major metabolic fuels in the proximal intestine and kidney, as glutamine for the liver and aspartate for skeletal muscle. All the tissues had high activities of glutaminase, glutamate dehydrogenase, and transaminases. At the same extracellular concentration of amino acids (2 mM) in a mixture of energy substrates, glutamine was the major metabolic fuel for the liver of the LMB, glutamine and glutamate for the proximal intestine and kidneys, and aspartate for the skeletal muscle. Glutamine plus glutamate plus aspartate generated 60–70% of ATP in LMB tissues.

中文翻译：

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大口黑鲈（Micropterus salmoides）组织中能量底物的氧化。

这项研究检验了以下假设：在大嘴鲈（LMB，一种肉食性鱼类）的组织中，氨基酸被氧化的速率比葡萄糖和棕榈酸酯的氧化速率更高，而棕榈酸酯被氧化。从LMB分离出的肝，近肠，肾脏和骨骼肌的切片（10至50 mg）在含氧的Krebs-Henseleit碳酸氢盐缓冲液（pH 7.4，含5 mM d-葡萄糖）中于26°C孵育2 h。d - [U- ¹⁴ C]葡萄糖，2mM的升丙氨酸加升- [U- ¹⁴ C]丙氨酸，2毫升天冬氨酸加升- [U- ¹⁴ C]天冬氨酸盐，2毫升-谷氨酸加升- [U- ¹⁴C]谷氨酸盐，2 mM 1-谷氨酰胺加1- [U- ¹⁴ C]谷氨酰胺，2 mM 1-亮氨酸加1- [U- ¹⁴ C]亮氨酸或2 mM棕榈酸酯加[U- ¹⁴ C]棕榈酸酯。在平行实验中，将组织与[U- ¹⁴ C]标记的示踪剂和未标记底物[丙氨酸，天冬氨酸，谷氨酸，谷氨酰胺，亮氨酸和棕榈酸酯（各2 mM）加5 mM葡萄糖）的混合物一起孵育。收集^14个CO ₂以计算底物氧化速率。在单独的实验中，O ₂在存在单个或多种底物的情况下测量每种组织的消耗。还测量了关键代谢酶的活性。结果表明，肝脏和骨骼肌氧化葡萄糖和棕榈酸酯化为CO _2的能力有限由于肉碱棕榈酰基转移酶-I，己糖激酶和丙酮酸脱氢酶的活性低，在单个或混合底物的情况下产生ATP。在存在单个底物的情况下，所有组织都积极地氧化了每种氨基酸。在存在底物混合物的情况下，谷氨酰胺和谷氨酸盐是近端肠和肾脏的主要代谢燃料，谷氨酰胺用于肝脏，天门冬氨酸用于骨骼肌。所有组织均具有高活性的谷氨酰胺酶，谷氨酸脱氢酶和转氨酶。在能量底物混合物中具有相同的细胞外氨基酸浓度（2 mM）时，谷氨酰胺是LMB肝脏的主要代谢燃料，谷氨酰胺和谷氨酸是近端肠道和肾脏的主要代谢燃料，而天冬氨酸是骨骼肌的主要代谢燃料。