Which of the following is the best evidence for the lock and key hypothesis of enzyme action?

Options

A. All isolated enzymes have been identified as proteins
B. Enzymes determine the direction of a reaction
C. Enzymes are found in living organisms and speed up certain reactions
D. Compounds similar in structure to the substrate inhibit the reaction

Explanation

To answer the question "Which of the following is the best evidence for the lock and key hypothesis of enzyme action?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Lock and Key Hypothesis**: The lock and key hypothesis suggests that enzymes have specific active sites that fit perfectly with their corresponding substrates, similar to how a key fits into a lock. This means that only substrates with a complementary shape can bind to the enzyme.

2. **Identify the Role of Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in the body. They do this by forming an enzyme-substrate complex, which is crucial for the reaction to occur.

3. **Recognize the Importance of Structure**: The active site of an enzyme is specifically shaped to fit a particular substrate. This specificity is what allows enzymes to catalyze specific reactions.

4. **Evaluate the Options**: To determine which option provides the best evidence for the lock and key hypothesis, we need to look for a statement that emphasizes the structural compatibility between the enzyme and the substrate.

5. **Select the Correct Option**: The best evidence for the lock and key hypothesis is that "compounds with a similar structure to the substrate inhibit the reaction." This indicates that if a compound resembles the substrate, it can bind to the enzyme's active site and prevent the actual substrate from binding, supporting the idea of a specific fit.

### Final Answer:
The best evidence for the lock and key hypothesis of enzyme action is that "compounds with a similar structure to the substrate inhibit the reaction."

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