Name an antioxidant enzyme that requires selenium.

Glutathione peroxidase is an antioxidant enzyme that requires selenium for its activity. This enzyme plays a critical role in protecting cells from oxidative damage by reducing hydrogen peroxide and organic peroxides, which are harmful byproducts of metabolic processes. The presence of selenium is essential as it is incorporated into the enzyme's structure in the form of selenocysteine, which allows the enzyme to perform its catalytic function effectively. Selenium deficiency can lead to reduced levels and activity of glutathione peroxidase, resulting in an increased susceptibility to oxidative stress and potential damage to cells and tissues.

In contrast, while other enzymes such as superoxide dismutase and catalase are important for combating oxidative stress, they do not require selenium for their function. Lactate dehydrogenase is primarily involved in metabolic processes, specifically in the conversion of pyruvate to lactate, and does not have a role in antioxidant defense mechanisms. Therefore, glutathione peroxidase is uniquely identified as the selenium-dependent antioxidant enzyme among the choices provided.