Erythrocytes contain the Rapoport-Luebering shunt, in which 1,3-bisphosphoglycerate is converted to 2,3-bisphosphoglycerate (2,3-BPG) instead of proceeding through phosphoglycerate kinase. What is the metabolic cost of this detour to the red cell?
- A No energy cost, because 2,3-BPG is later reconverted to pyruvate with full ATP yield
- B Loss of two molecules of ATP per glucose, halting glycolysis entirely
- C Loss of one molecule of ATP per 1,3-BPG diverted, since the phosphoglycerate kinase step is bypassed ✓
- D Gain of one ATP per glucose, because bisphosphoglycerate mutase generates a high-energy intermediate
Correct answer: C. Loss of one molecule of ATP per 1,3-BPG diverted, since the phosphoglycerate kinase step is bypassed
Explanation
The phosphoglycerate kinase reaction normally transfers the acyl phosphate of 1,3-BPG to ADP, yielding ATP. When 2,3-BPG is formed instead, this ATP-generating step is skipped, so the red cell sacrifices one ATP per diverted molecule while gaining 2,3-BPG, which binds deoxygenated hemoglobin and shifts the oxygen dissociation curve right. 2,3-BPG is hydrolyzed to 3-PG by a phosphatase, recovering downstream ATP yield but never the skipped step.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.