An example of non-competitive inhibition is

Options

A. Succinic dehydrogenase by Malonic acid
B. Cytochrome oxidase by cyanide
C. hexokinase by glucose 6-phosphate
D. Carbonic anhydrase by carbon dioxide

Answer

To determine an example of non-competitive inhibition, we need to analyze the options provided and understand the concept of non-competitive inhibition.

### Step-by-Step Solution:

1. **Understanding Non-Competitive Inhibition**:
- Non-competitive inhibition occurs when an inhibitor binds to an enzyme at a site other than the active site. This binding changes the shape of the enzyme, preventing the substrate from effectively binding to the active site, regardless of the concentration of the substrate.

2. **Analyzing the Options**:
- **Option 1**: Succinic dehydrogenase by malonic acid.
- Malonic acid is a competitive inhibitor for succinic dehydrogenase, as it competes with succinate for the active site.

- **Option 2**: Cytochrome oxidase by cyanide.
- Cyanide acts as a non-competitive inhibitor for cytochrome oxidase, as it binds to the enzyme regardless of whether the substrate is present or not, inhibiting the enzyme's activity.

- **Option 3**: Hexokinase by glucose 6-phosphate.
- Glucose 6-phosphate is a product inhibitor for hexokinase and acts through feedback inhibition, which can be considered non-competitive in some contexts, but primarily it is competitive as it binds to the active site.

- **Option 4**: Carbonic anhydrase by carbon dioxide.
- Carbon dioxide does not act as an inhibitor for carbonic anhydrase; rather, it is a substrate for the enzyme.

3. **Identifying the Correct Answer**:
- Based on the analysis, **the second option, cytochrome oxidase by cyanide**, is the correct example of non-competitive inhibition.

### Final Answer:
The correct example of non-competitive inhibition is **cytochrome oxidase by cyanide**.

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