All of the following statements about glycolytic enzymes are true EXCEPT:

Explanation

## Analysis of Glycolytic Enzyme Properties ### Correct Statements (Options 0, 1, 2) **Key Point:** Hexokinase exhibits product inhibition by glucose-6-phosphate, a classic feedback mechanism that prevents excessive phosphorylation when G6P levels are high. **High-Yield:** Phosphofructokinase-1 (PFK-1) is the primary rate-limiting step of glycolysis and is activated by AMP (and ADP), signaling low energy status — this is a fundamental regulatory principle. **Key Point:** Pyruvate kinase is inhibited by both ATP (high energy signal) and acetyl-CoA (abundant biosynthetic precursor), preventing futile glucose breakdown when energy is abundant. ### The Incorrect Statement (Option 3) **Warning:** Aldolase does NOT catalyze a simple cleavage reaction. It is a **Class I aldolase** (in animals) that requires a **Schiff base intermediate** formed between the ketone group of fructose-1,6-bisphosphate and a lysine residue in the enzyme's active site. This is a covalent catalytic mechanism, not a cofactor-independent cleavage. **Mnemonic:** **AAAA** = **Aldolase Activates via Amino acid (Schiff base)**. The Schiff base is the critical intermediate. ### Comparison of Aldolase Mechanisms | Feature | Class I Aldolase (Animals) | Class II Aldolase (Bacteria) | |---------|---------------------------|------------------------------| | Cofactor requirement | None (covalent Schiff base) | Zn²⁺ metal ion | | Mechanism | Lysine residue forms imine | Metal coordinates substrate | | Intermediate | Schiff base (carbinoamine) | Zn-enamine | **Clinical Pearl:** Deficiency of aldolase B (fructose-1-phosphate aldolase) causes hereditary fructose intolerance, not a glycolysis defect per se, but demonstrates the physiologic importance of this enzyme family. [cite:Lehninger Principles of Biochemistry 8e Ch 14]