All of the following statements regarding glycolytic enzymes are correct EXCEPT:

## Glycolytic Enzyme Mechanisms ### Analysis of Each Statement | Enzyme | Statement | Accuracy | |--------|-----------|----------| | Hexokinase | Product inhibition by G6P | ✓ Correct | | PFK-1 | Rate-limiting; activated by AMP/ADP | ✓ Correct | | Pyruvate kinase | Final irreversible step; inhibited by acetyl-CoA, citrate | ✓ Correct | | Aldolase | Cleaves F-1,6-BP; requires NAD+ | ✗ **WRONG** | ### The Critical Error: Aldolase Cofactor **Key Point:** Aldolase is a Class I aldolase (in animals) that uses a **Schiff base mechanism** involving a lysine residue in the active site. It does **NOT** require NAD^+^ as a cofactor. **High-Yield:** Aldolase catalyzes a **non-oxidative cleavage** of fructose-1,6-bisphosphate into: - Dihydroxyacetone phosphate (DHAP) - Glyceraldehyde-3-phosphate (G3P) The mechanism involves: 1. Formation of a Schiff base (imine) between the substrate and an active-site lysine 2. Cleavage of the C3–C4 bond 3. Release of products **Warning:** Do not confuse aldolase with glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which **does** require NAD^+^ as an oxidizing cofactor in the next step of glycolysis. ### Why the Other Statements Are Correct **Hexokinase (Statement 1):** - Catalyzes: Glucose + ATP → Glucose-6-phosphate + ADP - Inhibited by product (G6P) — classic feedback inhibition - Traps glucose in the cell **PFK-1 (Statement 2):** - **Rate-limiting enzyme** of glycolysis - Allosterically activated by: AMP, ADP, F-2,6-BP (signals of low energy) - Allosterically inhibited by: ATP, citrate (signals of high energy) **Pyruvate kinase (Statement 3):** - Catalyzes: Phosphoenolpyruvate + ADP → Pyruvate + ATP - Final irreversible step - Inhibited by acetyl-CoA and citrate (signals of sufficient energy/biosynthetic precursors) **Mnemonic:** NAD^+^ is used in **oxidative steps** of glycolysis — remember **GAPDH** (Glyceraldehyde-3-phosphate DeHydrogenase) as the NAD^+^-dependent enzyme, not aldolase.