The enzyme which does not directly act upon the food substrate in the small intestine of man, is

Options

A. Amylase
B. Lipase
C. Enterokinase
D. Trypsin

Answer

To solve the question, we need to identify which enzyme does not directly act upon food substrates in the small intestine of humans. Let's analyze the options given:

1. **Amylase**:
- Function: Amylase is an enzyme that breaks down starches (carbohydrates) into simpler sugars like maltose and other disaccharides.
- Conclusion: Amylase acts directly on food substrates.

2. **Lipase**:
- Function: Lipase is an enzyme that breaks down fats into fatty acids and glycerol.
- Conclusion: Lipase acts directly on food substrates.

3. **Tyrokinase (likely a reference to Enterokinase)**:
- Function: Enterokinase (or tyrokinase) activates trypsinogen (an inactive form of trypsin) into trypsin. It does not act on food substrates directly but rather on another enzyme.
- Conclusion: Enterokinase does not act directly on food substrates.

4. **Trypsin**:
- Function: Trypsin is a proteolytic enzyme that breaks down proteins into smaller peptides.
- Conclusion: Trypsin acts directly on food substrates.

Based on the analysis, the enzyme that does not directly act upon food substrates in the small intestine is **Enterokinase (Tyrokinase)**.

### Final Answer:
The enzyme which does not directly act upon the food substrate in the small intestine of man is **Enterokinase (Tyrokinase)**.