Cho Jaiesoon, King Jason S, Qian Xun, Harwood Adrian J, Shears Stephen B
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Social Services, P.O. Box 12233, Research Triangle Park, NC 27709, USA.
Proc Natl Acad Sci U S A. 2008 Apr 22;105(16):5998-6003. doi: 10.1073/pnas.0710980105. Epub 2008 Apr 14.
The Rapoport-Luebering glycolytic bypass comprises evolutionarily conserved reactions that generate and dephosphorylate 2,3-bisphosphoglycerate (2,3-BPG). For >30 years, these reactions have been considered the responsibility of a single enzyme, the 2,3-BPG synthase/2-phosphatase (BPGM). Here, we show that Dictyostelium, birds, and mammals contain an additional 2,3-BPG phosphatase that, unlike BPGM, removes the 3-phosphate. This discovery reveals that the glycolytic pathway can bypass the formation of 3-phosphoglycerate, which is a precursor for serine biosynthesis and an activator of AMP-activated protein kinase. Our 2,3-BPG phosphatase activity is encoded by the previously identified gene for multiple inositol polyphosphate phosphatase (MIPP1), which we now show to have dual substrate specificity. By genetically manipulating Mipp1 expression in Dictyostelium, we demonstrated that this enzyme provides physiologically relevant regulation of cellular 2,3-BPG content. Mammalian erythrocytes possess the highest content of 2,3-BPG, which controls oxygen binding to hemoglobin. We determined that total MIPP1 activity in erythrocytes at 37 degrees C is 0.6 mmol 2,3-BPG hydrolyzed per liter of cells per h, matching previously published estimates of the phosphatase activity of BPGM. MIPP1 is active at 4 degrees C, revealing a clinically significant contribution to 2,3-BPG loss during the storage of erythrocytes for transfusion. Hydrolysis of 2,3-BPG by human MIPP1 is sensitive to physiologic alkalosis; activity decreases 50% when pH rises from 7.0 to 7.4. This phenomenon provides a homeostatic mechanism for elevating 2,3-BPG levels, thereby enhancing oxygen release to tissues. Our data indicate greater biological significance of the Rapoport-Luebering shunt than previously considered.
拉波波特-吕伯林糖酵解支路包含进化上保守的反应，这些反应生成2,3-二磷酸甘油酸（2,3-BPG）并使其去磷酸化。30多年来，这些反应一直被认为是单一酶——2,3-BPG合酶/2-磷酸酶（BPGM）的职责。在此，我们表明，盘基网柄菌、鸟类和哺乳动物含有另一种2,3-BPG磷酸酶，与BPGM不同，它去除3-磷酸基团。这一发现揭示了糖酵解途径可以绕过3-磷酸甘油酸的形成，3-磷酸甘油酸是丝氨酸生物合成的前体和AMP激活的蛋白激酶的激活剂。我们的2,3-BPG磷酸酶活性由先前鉴定的多肌醇多磷酸磷酸酶（MIPP1）基因编码，我们现在证明它具有双底物特异性。通过基因操纵盘基网柄菌中Mipp1的表达，我们证明该酶对细胞2,3-BPG含量具有生理相关的调节作用。哺乳动物红细胞中2,3-BPG含量最高，它控制氧气与血红蛋白的结合。我们确定，37摄氏度时红细胞中MIPP1的总活性为每升细胞每小时水解0.6 mmol 2,3-BPG，与先前发表的BPGM磷酸酶活性估计值相符。MIPP1在4摄氏度时具有活性，这揭示了其在输血用红细胞储存期间对2,3-BPG损失具有临床显著影响。人MIPP1对2,3-BPG的水解对生理性碱中毒敏感；当pH从7.0升至7.4时，活性降低50%。这一现象提供了一种稳态机制，用于提高2,3-BPG水平，从而增强氧气向组织的释放。我们的数据表明，拉波波特-吕伯林分流的生物学意义比以前认为的更大。
