**Core Concept**
Non-competitive enzyme inhibition is a type of enzyme inhibition where the inhibitor binds to a region of the enzyme that is not the active site, but affects the enzyme's activity by altering its conformation or by reducing its affinity for the substrate. This type of inhibition is characterized by a decrease in the maximum velocity (Vmax) of the enzyme reaction without affecting the Michaelis constant (Km).

**Why the Correct Answer is Right**
In non-competitive inhibition, the inhibitor binds to a region called the allosteric site, which is distinct from the active site where the substrate binds. This binding causes a conformational change in the enzyme, reducing its ability to bind to the substrate and increasing the Km. As a result, the Vmax of the enzyme reaction decreases, but the Km remains unchanged. This type of inhibition is often seen in feedback inhibition, where the product of a metabolic pathway inhibits an earlier step in the pathway to regulate its own production.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because non-competitive inhibition does not change the Km of the enzyme reaction, only the Vmax.
**Option B:** This statement is incorrect because competitive inhibition is a different type of inhibition where the inhibitor competes with the substrate for binding to the active site, increasing the Km.
**Option C:** This statement is incorrect because non-competitive inhibition is not the same as irreversible inhibition, where the inhibitor forms a covalent bond with the enzyme.

**Clinical Pearl / High-Yield Fact**
Non-competitive inhibition is an important mechanism of feedback regulation in metabolic pathways, where the product of a pathway inhibits an earlier step to regulate its own production and prevent excessive accumulation.

**Correct Answer:** C. Non-competitive inhibition decreases the Vmax without changing the Km.