Best Isotope for Metabolic Labeling of Glyceraldehyde-3-Phosphate Dehydrogenase

Which isotope below is best suited for metabolic labelling of glyceraldehyde-3 phospho-dehydrogenase?
(A) 14 C
(B) 125 I
(C) 32p
(D) 131 I

Correct Answer: (A) ¹⁴C (Carbon-14)

Introduction (Metabolic labeling of GAPDH)

Metabolic labeling is a powerful technique used in molecular biology to study biochemical pathways. It involves incorporating a radioactive isotope into biomolecules to trace their metabolism. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme in the glycolysis pathway, making ¹⁴C (Carbon-14) the most suitable isotope for its metabolic labeling.

Why is ¹⁴C the Best Choice?

Carbon-14 is a radioactive isotope of carbon, which is naturally present in organic molecules. Since GAPDH functions in glycolysis, where carbon-based sugars like glucose and glyceraldehyde-3-phosphate are metabolized, ¹⁴C can effectively trace the enzyme’s activity.

Advantages of Using ¹⁴C for Metabolic Labeling

✅ Direct Incorporation into Carbon-Based Metabolites – Since glycolysis involves carbon-containing molecules, ¹⁴C-labeled glucose or glyceraldehyde-3-phosphate can be used to trace metabolic pathways.
✅ Long Half-Life (5,730 years) – This ensures stability and accuracy in long-term experiments.
✅ Minimal Radiation Hazard – Compared to high-energy isotopes like ³²P or ¹³¹I, ¹⁴C emits weak beta radiation, making it safer to handle in biochemical studies.

Why Other Options Are Incorrect?

❌ ¹²⁵I (Iodine-125) – Used for protein labeling, particularly in thyroid research, but does not track carbon metabolism.
❌ ³²P (Phosphorus-32) – Used for studying DNA/RNA phosphorylation rather than carbon-based metabolic pathways.
❌ ¹³¹I (Iodine-131) – Primarily used in medical imaging and thyroid treatments, not for metabolic labeling in glycolysis.

Conclusion

For metabolic labeling of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), ¹⁴C (Carbon-14) is the most appropriate isotope due to its ability to integrate seamlessly into carbon-based metabolic pathways. Since GAPDH plays a crucial role in glycolysis, tracking its activity with a carbon isotope ensures accurate insights into glucose metabolism and energy production.

Unlike phosphorus or iodine isotopes, which are better suited for nucleic acid or protein studies, ¹⁴C allows real-time monitoring of carbon flux through metabolic pathways, making it an invaluable tool for biochemical research, enzyme kinetics, and metabolic engineering. Additionally, its long half-life ensures reliable long-term studies without rapid decay affecting the experiment.

Thus, ¹⁴C-labeled glucose or glyceraldehyde-3-phosphate provides a direct and efficient way to trace GAPDH activity, helping researchers understand disease mechanisms, drug responses, and metabolic regulation at a molecular level.

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