Mazzola Jennifer L, Sirover Michael A
Department of Pharmacology, Temple University School of Medicine, 3420 N. Broad Street, Philadelphia, PA 19140, USA.
Biochim Biophys Acta. 2003 Jun 20;1622(1):50-6. doi: 10.1016/s0304-4165(03)00117-x.
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was considered a classical glycolytic protein involved exclusively in cytosolic energy production. However, recent evidence suggests that it is a multifunctional protein displaying diverse activities distinct from its conventional metabolic role. These new roles for GAPDH may be dependent on its subcellular localization, oligomeric state or on the proliferative state of the cell. GAPDH is encoded by a single gene without alternate splicing. The regulatory mechanisms are unknown through which an individual GAPDH molecule fulfills its non-glycolytic functions or is targeted to a specific intracellular localization. Accordingly, as a first step to elucidate these subcellular regulatory mechanisms, we examined the interrelationship between the intracellular expression of the GAPDH protein and its glycolytic function in normal human fetal and senior cells. GAPDH localization was determined by immunoblot analysis. Enzyme activity was quantitated by in vitro biochemical assay. We now report that the subcellular expression of GAPDH was independent of its classical glycolytic function. In particular, in both fetal and senior cells, considerable GADPH protein was present in intracellular domains characterized by significantly reduced catalysis. Gradient analysis indicated that this lower activity was not due to the dissociation of tetrameric GAPDH. These results suggest that human cells contain significant intracellular levels of enzymatically inactive GAPDH which is age-independent. The possibility is considered that the functional diversity of GAPDH may be mediated either by posttranslational alteration or by subcellular protein:protein and/or protein:nucleic acid interactions.
甘油醛-3-磷酸脱氢酶（GAPDH）曾被认为是一种经典的糖酵解蛋白，仅参与胞质能量生成。然而，最近的证据表明它是一种多功能蛋白，具有与其传统代谢作用不同的多种活性。GAPDH的这些新作用可能取决于其亚细胞定位、寡聚状态或细胞的增殖状态。GAPDH由单个基因编码，无可变剪接。目前尚不清楚单个GAPDH分子是通过何种调节机制来实现其非糖酵解功能或靶向特定细胞内定位的。因此，作为阐明这些亚细胞调节机制的第一步，我们研究了正常人类胎儿和老年细胞中GAPDH蛋白的细胞内表达与其糖酵解功能之间的相互关系。通过免疫印迹分析确定GAPDH的定位。通过体外生化测定对酶活性进行定量。我们现在报告，GAPDH的亚细胞表达与其经典糖酵解功能无关。特别是，在胎儿和老年细胞中，相当数量的GADPH蛋白存在于催化作用显著降低的细胞内区域。梯度分析表明，这种较低的活性不是由于四聚体GAPDH的解离。这些结果表明，人类细胞中含有大量酶活性无活性的GAPDH，且与年龄无关。人们认为，GAPDH的功能多样性可能是由翻译后修饰或亚细胞蛋白-蛋白和/或蛋白-核酸相互作用介导的。
