A slow enzyme isn't always a denatured one
- The idea
- Predict
- See it
- Why
- Check
The idea
“If an enzyme slows down or stops working, it must have denatured.”
Heat and pH really can denature enzymes. So denaturation gets blamed for every slowdown.
The short version
The mistake: If an enzyme slows down or stops working, it must have denatured.
What's actually true: Cold, a mild pH shift or an inhibitor can slow a folded enzyme. Normal substrate binding means the active site kept its shape.
- An enzyme binds substrate, then lowers the activation energy. Either step can slow while the protein keeps its shape.
- Denaturation means the protein unfolds and its active site loses its shape, so substrate no longer fits. Extreme heat or pH can do this.
- Other things slow a folded enzyme. Cold slows molecules. A mild pH shift can change the charge on a side chain the reaction needs. An inhibitor can block the active site.
On the exam: Before you say denatured, check binding. Normal binding means the active site kept its shape.