van Raamsdonk W, Smit-Onel M J, Diegenbach P C
Department of Experimental Zoology, University of Amsterdam.
Acta Histochem. 1993 Dec;95(2):129-38. doi: 10.1016/S0065-1281(11)80251-5.
To study the interactions between the citrate cycle and amino acid metabolism in zebrafish spinal motoneurons, we composed enzyme histochemical profiles from the activities of NAD-linked isocitrate dehydrogenase (NAD-ICDH), glutamate dehydrogenase (GDH), succinate dehydrogenase (SDH) and glucose 6-phosphate dehydrogenase (G6PDH). The enzyme assays were performed on serially-sectioned motoneuron somata. The motoneurons were identified by retrograde tracing from the trunk muscle and classified, on the basis of their location in the motor column, as those innervating the white, fast glycolytic fibers (WMNs) or those innervating the red and intermediate slow oxidative fibers (RIMNs). We found the following relationships between enzyme activities in WMNs: GDH correlates with G6PDH activity (r = 0.31; p = 0.02) and NAD-ICDH correlates with GDH activity (r = 0.37; p < 0.01); correlations between NAD-ICDH and SDH and between SDH and GDH are not significant. In RIMNs we found correlations between NAD-ICDH and SDH (r = 0.34; p = 0.03), between NAD-ICDH and GDH (r = 0.41; p < 0.01) and between GDH and SDH (r = 0.50; p < 0.01); the correlation between GDH and G6PDH is not significant. The differences in metabolic profiles between WMNs and RIMNs can be explained in the following way: in WMNs, alpha-ketoglutarate is drawn off from the citrate cycle and is used in amino acid metabolism whereas in RIMNs the removal of alpha-ketoglutarate from the cycle is balanced by formation of alpha-ketoglutarate. The data suggest that the functional role of the citrate cycle differs in the two motoneuron populations: in RIMNs energy generation predominates but in WMNs a role in biosyntheses seems most important.
为了研究斑马鱼脊髓运动神经元中柠檬酸循环与氨基酸代谢之间的相互作用，我们根据烟酰胺腺嘌呤二核苷酸（NAD）连接的异柠檬酸脱氢酶（NAD-ICDH）、谷氨酸脱氢酶（GDH）、琥珀酸脱氢酶（SDH）和葡萄糖6-磷酸脱氢酶（G6PDH）的活性构建了酶组织化学图谱。酶活性测定在连续切片的运动神经元胞体上进行。通过从躯干肌肉逆行追踪来识别运动神经元，并根据它们在运动柱中的位置，将其分为支配白色快速糖酵解纤维的运动神经元（WMNs）或支配红色和中间慢氧化纤维的运动神经元（RIMNs）。我们发现WMNs中酶活性之间存在以下关系：GDH与G6PDH活性相关（r = 0.31；p = 0.02），NAD-ICDH与GDH活性相关（r = 0.37；p < 0.01）；NAD-ICDH与SDH之间以及SDH与GDH之间的相关性不显著。在RIMNs中，我们发现NAD-ICDH与SDH之间（r = 0.34；p = 0.03）、NAD-ICDH与GDH之间（r = 0.41；p < 0.01）以及GDH与SDH之间（r = 0.50；p < 0.01）存在相关性；GDH与G6PDH之间的相关性不显著。WMNs和RIMNs之间代谢图谱的差异可以用以下方式解释：在WMNs中，α-酮戊二酸从柠檬酸循环中被提取出来并用于氨基酸代谢，而在RIMNs中，α-酮戊二酸从循环中的去除通过α-酮戊二酸的形成得到平衡。数据表明，柠檬酸循环在这两种运动神经元群体中的功能作用不同：在RIMNs中能量产生占主导，但在WMNs中，其在生物合成中的作用似乎最为重要。
