Enzyme was first isolated by

Options

A. Kuhne
B. Sumner
C. Payen and Persoz
D. Buchner.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks who first isolated an enzyme. We need to identify the correct scientist from the given options.

2. **Analyzing the Options**: The options provided are:
- Crony
- Semner
- Payan
- Persos
- Bueschner

3. **Researching Historical Context**:
- Eduard Bueschner is known for his work with yeast extracts and fermentation.
- In 1897, he demonstrated that yeast extracts could ferment sugar into alcohol, which indicated that fermentation was due to certain molecules (enzymes) that could function outside of the cells.

4. **Identifying the First Isolated Enzyme**:
- Bueschner isolated the enzyme urease in crystalline form, which was significant as it was one of the first enzymes to be isolated.

5. **Reviewing Other Scientists**:
- Kuhni discovered trypsin from pancreatic juice.
- Semner was noted for demonstrating that enzymes can be crystallized.
- Payan and Prusos are known for their work with diastase.

6. **Concluding the Answer**: Based on the historical context and the contributions of each scientist, the correct answer to the question "Enzyme was first isolated by" is **Bueschner**.

### Final Answer:
The enzyme was first isolated by **Bueschner**.

---