Which inactivates an enzyme by occupying its active site ?

Options

A. competitive inhinition
B. allosteric inhibitor
C. non-competitive inhibitor
D. all of these above

Answer

To determine which process inactivates an enzyme by occupying its active site, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Enzyme Function**: Enzymes are biological catalysts that speed up biochemical reactions. They have a specific region called the active site where substrates bind to undergo a reaction.

2. **Active Site and Substrate Interaction**: The active site of an enzyme is specifically shaped to fit a particular substrate. When the substrate binds to the active site, it forms an enzyme-substrate complex, leading to a chemical reaction that produces products.

3. **Introduction of Inhibitors**: Sometimes, other molecules can interfere with the enzyme's ability to bind to its substrate. These molecules can either bind to the active site or another part of the enzyme.

4. **Competitive Inhibition**: In competitive inhibition, a molecule that resembles the substrate competes for the active site of the enzyme. When this inhibitor occupies the active site, the actual substrate cannot bind, leading to decreased enzyme activity.

5. **Example of Competitive Inhibition**: A classic example is the enzyme succinate dehydrogenase, which acts on succinate. Malonate, a molecule similar in structure to succinate, can bind to the active site of succinate dehydrogenase, preventing succinate from binding and thus inhibiting the enzyme's activity.

6. **Conclusion**: The process that inactivates an enzyme by occupying its active site is called **competitive inhibition**.

### Final Answer:
**Competitive Inhibition**

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