Which one of the following statements is incorrect about enzyme catalysis?

Options

A. Enzymes are mostly proteinous in nature
B. Enzyme action is specific
C. Enzymes are denaturated by UV-rays and at high temperature
D. Enzymes are least reactive at optimum temperature

Explanation

To determine which statement about enzyme catalysis is incorrect, we will analyze each of the provided statements one by one.

### Step 1: Analyze the first statement
**Statement:** Enzymes are mostly proteinous in nature.
**Analysis:** This statement is correct. Most enzymes are indeed proteins, which are made up of amino acids.

### Step 2: Analyze the second statement
**Statement:** Enzyme action is specific.
**Analysis:** This statement is also correct. Enzymes are known for their specificity, meaning that each enzyme typically catalyzes a specific reaction or acts on a specific substrate.

### Step 3: Analyze the third statement
**Statement:** Enzymes are denatured by UV rays at high temperature.
**Analysis:** This statement is somewhat misleading. While enzymes can be denatured by high temperatures, UV rays can also cause denaturation. However, the primary factor for denaturation is high temperature, and UV rays are not the typical cause of denaturation in enzymes. This statement is not entirely incorrect but may not be the best representation of enzyme denaturation.

### Step 4: Analyze the fourth statement
**Statement:** Enzymes are least reactive at optimum temperature.
**Analysis:** This statement is incorrect. Enzymes are most reactive at their optimum temperature, which is typically around 37 degrees Celsius for many human enzymes. Therefore, this statement contradicts the established understanding of enzyme activity.

### Conclusion
After analyzing all the statements, the incorrect statement about enzyme catalysis is: **"Enzymes are least reactive at optimum temperature."**

---