Which of the following conversion are done by enterokinase of the intestine?

Options

A. pepsinogen ito pepsin
B. trypsinogen into trypsin
C. caseinogen into casein
D. proteins into polypeptides

Explanation

To solve the question regarding the conversions done by enterokinase in the intestine, we will analyze each option provided and identify the correct conversion that enterokinase catalyzes.

### Step-by-Step Solution:

1. **Understanding Enterokinase**:
- Enterokinase is an enzyme secreted by the intestinal mucosa. Its primary role is to activate certain digestive enzymes that are secreted in inactive forms.

2. **Analyzing the Options**:
- **Option 1: Pepsinogen into Pepsin**:
- Pepsinogen is secreted by the stomach, not the intestine, and is activated by hydrochloric acid (HCl) in the stomach to form pepsin. Therefore, this conversion is not catalyzed by enterokinase.

- **Option 2: Trypsinogen into Trypsin**:
- Trypsinogen is a pancreatic enzyme that is secreted in an inactive form. Enterokinase activates trypsinogen into trypsin in the intestine. This is the correct conversion that enterokinase catalyzes.

- **Option 3: Caseinogen into Casein**:
- Caseinogen is not an inactive form of casein; casein is a milk protein. There is no conversion of caseinogen into casein that involves enterokinase, making this option incorrect.

- **Option 4: Proteins into Polypeptides**:
- While proteins are broken down into polypeptides during digestion, this conversion is not specifically catalyzed by enterokinase. It involves other proteolytic enzymes, so this option is also incorrect.

3. **Conclusion**:
- Based on the analysis, the only correct conversion that enterokinase catalyzes is the conversion of trypsinogen into trypsin. Therefore, the answer is **Option 2**.

### Final Answer:
The conversion done by enterokinase of the intestine is **Trypsinogen into Trypsin** (Option 2).