Enterokinase activates
(a) pepsin
(b) trypsin
(c) chymotrypsin
(d) trypsinogen

Options

A. pepsin
B. trypsin
C. chymotrypsin
D. trypsinogen

Explanation

To solve the question regarding which enzyme is activated by enterokinase, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Enterokinase**:
- Enterokinase, also known as enteropeptidase, is an enzyme secreted by the intestinal glands, specifically from the crypts of Lieberkühn.

2. **Function of Enterokinase**:
- The primary role of enterokinase is to activate certain proenzymes that are secreted by the pancreas. It does this after food has passed through the stomach and enters the small intestine.

3. **Identifying the Proenzyme**:
- Among the options provided (pepsin, trypsin, chymotrypsin, trypsinogen), we need to identify which one is a proenzyme that enterokinase acts upon.
- Pepsin is an active enzyme that digests proteins in the stomach and is not activated by enterokinase.
- Trypsin is the active form of the enzyme that is involved in protein digestion.
- Chymotrypsin is another digestive enzyme that is activated by trypsin.
- Trypsinogen is the inactive precursor (proenzyme) of trypsin.

4. **Activation Process**:
- Enterokinase specifically acts on trypsinogen, converting it into its active form, trypsin. This activation is crucial as trypsin then activates other pancreatic enzymes, including chymotrypsin.

5. **Conclusion**:
- Therefore, the correct answer to the question is (d) trypsinogen, as it is the proenzyme that enterokinase activates.

### Final Answer:
**(d) trypsinogen**