Expand IUB and write about its most significant contribution.

Explanation

### Step-by-Step Solution:

1. **Expand IUB**:
- IUB stands for the **International Union of Biochemistry**.

2. **Significant Contribution of IUB**:
- One of the most significant contributions of the International Union of Biochemistry is the establishment of the **Enzyme Commission** in **1961**.
- The Enzyme Commission was responsible for developing basic principles for the **classification** and **nomenclature** of enzymes.
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