**Core Concept**
The brain is highly susceptible to oxidative stress due to its high metabolic rate and high content of polyunsaturated fatty acids. To mitigate this, the brain has developed various mechanisms to protect itself from free radical injury, including the action of specific enzymes.

**Why the Correct Answer is Right**
Superoxide dismutase (SOD) is a key enzyme responsible for protecting the brain from free radical injury. It catalyzes the dismutation of the superoxide (O2−) radical into either ordinary molecular oxygen (O2) or hydrogen peroxide (H2O2). This reaction is crucial in preventing the formation of more harmful reactive oxygen species (ROS) that can damage cellular components. SOD is present in several forms, including copper-zinc SOD (SOD1), manganese SOD (SOD2), and iron SOD (SOD3), each localized in different cellular compartments.

**Why Each Wrong Option is Incorrect**
* **Option A:** Catalase is an enzyme that converts hydrogen peroxide (H2O2) into water and oxygen, but it does not directly protect the brain from free radical injury by scavenging superoxide radicals.
* **Option B:** Glutathione peroxidase is an enzyme that reduces lipid hydroperoxides to their corresponding alcohols and reduces free hydrogen peroxide to water. While it plays a role in antioxidant defense, it is not primarily responsible for protecting the brain from free radical injury.
* **Option D:** Glutathione S-transferase is an enzyme involved in the conjugation of glutathione with electrophilic compounds, but it is not a primary enzyme for protecting the brain from free radical injury.

**Clinical Pearl / High-Yield Fact**
Mnemonics to remember the antioxidant enzymes include: "SOD (Superoxide Dismutase) saves the day" or "CAT (Catalase) converts H2O2, GPx (Glutathione Peroxidase) reduces H2O2, and GST (Glutathione S-transferase) conjugates glutathione."

**Correct Answer: C. Superoxide dismutase (SOD)**