GLUTAMINE AND GLUCOSE-METABOLISM DURING THYMOCYTE PROLIFERATION - PATHWAYS OF GLUTAMINE AND GLUTAMATE METABOLISM
GLUTAMINE AND GLUCOSE-METABOLISM DURING THYMOCYTE PROLIFERATION - PATHWAYS OF GLUTAMINE AND GLUTAMATE METABOLISM
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DOI：
10.1042/bj2280353
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发表时间：
1985-01-01
影响因子：
4.1
通讯作者：
BRAND, K
中科院分区：
文献类型：
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作者：
BRAND, K
将增殖培养的大鼠胸腺细胞的能量代谢与新鲜制备的非增殖静止细胞的能量代谢进行了比较。大鼠胸腺细胞在伴刀豆球蛋白A和Lymphocult T（白细胞介素 - 2）刺激后进入增殖周期，在60小时时DNA合成速率达到最大。与孵育的静止胸腺细胞相比，孵育的增殖胸腺细胞的葡萄糖代谢增加了53倍；所利用的葡萄糖有90%转化为乳酸，而静止细胞仅有56%代谢为乳酸。然而，后者将27%的葡萄糖氧化为二氧化碳，而增殖细胞仅为1.1%。增殖胸腺细胞中己糖激酶、6 - 磷酸果糖激酶、丙酮酸激酶和醛缩酶的活性分别增加了12倍、17倍、30倍和24倍，而丙酮酸氧化速率仅提高了3倍。增殖胸腺细胞中丙酮酸降解能力相对较低可能是这些细胞几乎将葡萄糖完全转化为乳酸的原因。大鼠胸腺细胞在增殖过程中谷氨酰胺的利用增加了8倍。谷氨酰胺代谢的主要终产物是谷氨酸、天冬氨酸、二氧化碳和氨。在产物中谷氨酰胺的碳和氮得到了完全回收。进入柠檬酸循环的由磷酸依赖性谷氨酰胺酶形成的谷氨酸量在增殖细胞中增加了5倍；76%通过高活性的天冬氨酸氨基转移酶转化为2 - 酮戊二酸，其余24%通过谷氨酸脱氢酶转化。对于静止细胞，得到了相同的百分比（75%和25%）。谷氨酰胺酶、谷氨酸脱氢酶和天冬氨酸氨基转移酶的最大活性在增殖细胞中分别增加了3倍、12倍和6倍；在柠檬酸循环中代谢的谷氨酸有32%以二氧化碳形式回收，61%以天冬氨酸形式回收。在静止细胞中，这一比例分别为41%和59%，在有丝分裂原刺激的细胞中分别为39%和65%。添加葡萄糖（4 mM）或苹果酸（2 mM）强烈降低了增殖胸腺细胞对谷氨酰胺的利用速率以及谷氨酸向2 - 酮戊二酸的转化速率，并且还影响了谷氨酸进一步代谢的途径。添加2 mM丙酮酸没有改变增殖胸腺细胞对谷氨酰胺的利用速率，但显著降低了谷氨酸之后阶段的代谢速率。在有丙酮酸存在的情况下乙酰辅酶A的形成可能解释了增殖胸腺细胞中谷氨酸相对增强的氧化为二氧化碳（56%）的现象。
Energy metabolism in proliferating cultured rat thymocytes was compared with that of freshly prepared non-proliferating resting cells. Cultured rat thymocytes enter a proliferative cycle after stimulation by concanavalin A and Lymphocult T (interleukin-2), with maximal rates of DNA synthesis at 60 h. Compared with incubated resting thymocytes, glucose metabolism by incubated proliferating thymocytes was increased 53-fold; 90% of the glucose utilized was converted into lactate, whereas resting cells metabolized only 56% to lactate. However, the latter oxidized 27% of glucose to CO2, as opposed to 1.1% by the proliferating cells. Activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and aldolase in proliferating thymocytes were increased 12-, 17-, 30- and 24-fold, respectively, whereas the rate of pyruvate oxidation was enhanced only 3-fold. The relatively low capacity of pyruvate degradation in proliferating thymocytes might be the reason for almost complete conversion of glucose into lactate by these cells. Glutamine utilization by rat thymocytes was 8-fold increased during proliferation. The major end products of glutamine metabolism are glutamate, asparatate, CO2 and ammonia. A complete recovery of glutamine carbon and nitrogen in the products was obtained. The amount of glutamate formed by phosphate-dependent glutaminase which entered the citric acid cycle was enhanced 5-fold in the proliferating cells; 76% was converted into 2-oxoglutarate by aspartate aminotransferase, present in high activity, and the remaining 24% by glutamate dehydrogenase. With resting cells the same percentages were obtained (75 and 25). Maximal activities of glutaminase, glutamate dehydrogenase and aspartate aminotransferase were increased 3-, 12- and 6-fold, respectively, in proliferating cells; 32% of the glutamate metabolized in the citric acid cycle was recovered in CO2 and 61% in aspartate. In resting cells this proportion was 41% and 59%, and in mitogen-stimulated cells 39% and 65%, respectively. Addition of glucose (4 mM) or malate (2 mM) strongly decreased the rates of glutamine utilization and glutamate conversion into 2-oxoglutarate by proliferating thymocytes and also affected the pathways of further glutamate metabolism. Addition of 2 mM-pyruvate did not alter the rate of glutamine utilization by proliferating thymocytes, but decreased the rate of metabolism beyond the stage of glutamate significantly. Formation of acetyl-CoA in the presence of pyruvate might explain the relatively enhanced oxidation of glutamate to CO2 (56%) by proliferating thymocytes.