Which of the following correctly pairs a glycolytic enzyme with its cofactor requirement?

Explanation

## Cofactor Requirements in Glycolysis **Key Point:** Different glycolytic enzymes require specific organic cofactors (NAD⁺, ATP, ADP) or metal ions (Mg²⁺, K⁺, Zn²⁺) for catalytic activity. Pyruvate kinase requires both Mg²⁺ and K⁺ as essential cofactors. ### Cofactor Requirements of Major Glycolytic Enzymes | Enzyme | Cofactor/Ion | Function | |--------|--------------|----------| | Hexokinase | Mg²⁺ | Stabilizes ATP and facilitates phosphoryl transfer | | Phosphofructokinase-1 | Mg²⁺ | Stabilizes ATP and ADP | | Glyceraldehyde-3-phosphate dehydrogenase | NAD⁺, Pi, CoA | Oxidation of G3P; NAD⁺ is the electron acceptor | | Phosphoglycerate kinase | Mg²⁺, ADP | ATP generation; Mg²⁺ stabilizes substrates | | Pyruvate kinase | Mg²⁺, K⁺, Mn²⁺ | **Mg²⁺ and K⁺ are essential cofactors** | | Enolase | Mg²⁺ | Catalyzes dehydration of 2-phosphoglycerate | **High-Yield:** Pyruvate kinase is unique among glycolytic enzymes in that it requires both Mg²⁺ and K⁺ as obligatory cofactors. This is a frequently tested detail in NEET PG biochemistry. **Mnemonic:** **PK Needs MgK** — Pyruvate Kinase requires Magnesium and Potassium. ### Why Each Enzyme Needs Its Specific Cofactor 1. **Metal ions (Mg²⁺, K⁺, Mn²⁺)**: Stabilize substrate binding, facilitate phosphoryl transfer, and maintain enzyme conformation. 2. **NAD⁺**: Acts as an electron acceptor in oxidation-reduction reactions (e.g., G3P dehydrogenase). 3. **ATP/ADP**: Substrates and cofactors in phosphoryl transfer reactions. **Clinical Pearl:** Deficiency of Mg²⁺ or K⁺ impairs glycolytic flux and ATP production, leading to muscle weakness, cardiac arrhythmias, and metabolic dysfunction. Hypokalemia and hypomagnesemia are common in chronic diarrhea, diuretic use, and malnutrition.