The reactions of the phosphorylated pathway of L-serine biosynthesis: thermodynamic relationships in rat liver in vivo.
The reactions of the phosphorylated pathway of L-serine biosynthesis: thermodynamic relationships in rat liver in vivo.
复制标题
L-丝氨酸生物合成磷酸化途径的反应：体内大鼠肝脏的热力学关系。
DOI：
10.1016/0003-9861(86)90206-7
复制
发表时间：
1986
影响因子：
3.9
通讯作者：
K. Lund
中科院分区：
文献类型：
--
作者：
R. Guynn;D. K. Merrill;K. Lund
在大鼠肝脏中测定了L-丝氨酸生物合成磷酸化途径酶的诱导对反应之间热力学关系的影响。根据正常和低蛋白饲料喂养2周的动物冻存肝脏中适当代谢物的浓度计算所涉及的反应的质量作用率。将这些比率与之前在生理条件下测定的相同反应的平衡常数和先前在兔身上获得的结果进行了比较。正常大鼠和兔之间的热力学关系如预期的那样不同，因为前者的l-丝氨酸生物合成酶的活性明显较低。尽管整个途径的ΔG在大鼠和兔中几乎相同(分别为−5.8和−5.5千卡/摩尔)，但ΔG在反应中的分布是不同的。在大鼠肝脏中，该途径的不平衡几乎平均地分为l-磷酸丝氨酸磷酸酶(EC 3.1.3.3)步骤和另外两个反应[d-3-磷酸甘油脱氢酶(EC 1.1.1.95)和l-磷酸丝氨酸转氨酶(EC 2.6.1.52)]，而在兔中，磷酸酶反应几乎占整个ΔG的比例。然而，给大鼠喂低蛋白饲料，d-3-磷酸甘油脱氢酶的活性是12倍，l-磷酸丝氨酸氨基转移酶的活性是20倍，l-磷酸丝氨酸磷酸转移酶的活性是2倍。在该途径的诱导下，组织中出现了L-磷酸丝氨酸，肝脏中的丝氨酸升高了3倍多，大鼠肝脏中的Δ-GIN模式与兔接近。
The effect of the induction of the enzymes of the phosphorylated pathway ofl-serine biosynthesis on the thermodynamic relationships among the reactions has been determined in rat liverin vivo. The mass action ratios of the reactions involved were calculated from the concentrations of appropriate metabolites in freeze-clamped liver from animals fed normal and low-protein diets for 2 weeks. These ratios were compared with the equilibrium constants of the same reactions previously determined under physiological conditions and the results previously obtained in the rabbit. The thermodynamic relationships in the pathway were different between the normal rat and rabbit as might have been expected, because of the significantly lower activities of thel-serine biosynthetic enzymes in the former animal. Although the ΔGfor the overall pathway is nearly identical in the rat and rabbit (−5.8versus−5.5 kcal/mol, respectively), the distribution of ΔGamong the reactions is different. The disequilibrium in the pathway in rat liver is nearly equally divided between thel-phosphoserine phosphatase (EC 3.1.3.3) step and the other two reactions [d-3-phosphoglycerate dehydrogenase (EC 1.1.1.95) andl-phosphoserine aminotransferase (EC 2.6.1.52)], whereas in rabbit the phosphatase reaction accounts for nearly the entire ΔG. Feeding the rat a low protein diet, however, induced the activity ofd-3-phosphoglycerate dehydrogenase 12-fold, that ofl-phosphoserine aminotransferase 20-fold, and that ofl-phosphoserine phosphatase 2-fold. With the induction of the pathway,l-phosphoserine appeared in the tissue, there was a more than 3-fold rise inl-serine in the liver, and the pattern of ΔGin the rat liver approached that in the rabbit.