García-Salguero L, Lupiáñez J A
Departamento de Bioquímica y Biología Molecular, Universidad de Granada, Spain.
Mol Cell Biochem. 1989 Oct 31;90(2):99-110. doi: 10.1007/BF00221209.
The adaptive response of renal metabolism of glucose was studied in isolated rat proximal and distal renal tubules after a high protein-low carbohydrate diet administration. This nutritional situation significantly stimulated the gluconeogenic activity in the renal proximal tubules (about 1.5 fold at 48 hours) due, in part, to a marked increase in the fructose 1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK) activities. In this tubular fragment, FBPase activity increased only at subsaturating fructose 1,6-bisphosphate concentration (30% at 48 hours) which involved a significant decrease in the Km (31%) for its substrate without changes in the Vmax. This enzymatic behaviour is probably related to modifications in the activity of the enzyme already present in the renal cells. Proximal PEPCK activity progressively increased at all substrate concentrations (almost 2 fold at 48h of high protein diet) which brought about changes in Vmax without changes in Kim. These changes are in agreement with variations in the cellular concentration of the enzyme. Neither gluconeogenesis nor the gluconeogenic enzymes changed in the distal fractions of the renal tubules. On the other hand, a high protein diet did not apparently modify the glycolytic ability in any fragment of the nephron, although a significant increase in the phosphofructokinase (PFK) and pyruvate kinase (PK) activities was found in the distal renal tubules. This short term regulation involved a significant decrease from 24 hours in the Km value of distal PFK (almost 40%) without changes in Vmax. The kinetic behaviour of distal PK was mixed. In the first 24h after high protein diet a significant decrease in the Km for phosphoenolpyruvate was found (30%) without variation in the Vmax, however during the second 24 hours the activity of this glycolytic enzyme increased significantly (almost 1.3 fold) without modifications in its Km value. On the contrary, this nutritional state did not modify the kinetic behaviour of any glycolytic enzyme in the proximal regions of the renal tubules.
在给予高蛋白低碳水化合物饮食后，对分离的大鼠近端和远端肾小管中葡萄糖的肾脏代谢适应性反应进行了研究。这种营养状况显著刺激了近端肾小管中的糖异生活性（48小时时约为1.5倍），部分原因是果糖1,6 - 二磷酸酶（FBPase）和磷酸烯醇丙酮酸羧激酶（PEPCK）活性显著增加。在这个肾小管片段中，FBPase活性仅在亚饱和果糖1,6 - 二磷酸浓度下增加（48小时时增加30%），这涉及到其底物的Km显著降低（31%），而Vmax没有变化。这种酶的行为可能与肾细胞中已存在的酶活性的改变有关。近端PEPCK活性在所有底物浓度下都逐渐增加（高蛋白饮食48小时时几乎增加2倍），这导致Vmax发生变化，而Km没有变化。这些变化与该酶的细胞浓度变化一致。肾小管远端部分的糖异生及糖异生酶均未改变。另一方面，高蛋白饮食显然未改变肾单位任何片段中的糖酵解能力，尽管在远端肾小管中发现磷酸果糖激酶（PFK）和丙酮酸激酶（PK）活性显著增加。这种短期调节涉及远端PFK的Km值从24小时起显著降低（几乎40%），而Vmax没有变化。远端PK的动力学行为较为复杂。高蛋白饮食后的前24小时，磷酸烯醇丙酮酸的Km显著降低（30%），Vmax没有变化，然而在第二个24小时期间，这种糖酵解酶的活性显著增加（几乎1.3倍），而其Km值没有改变。相反，这种营养状态未改变近端肾小管中任何糖酵解酶的动力学行为。
