Which antioxidant system is involved in regeneration by thioredoxin reductase?

The correct choice, ascorbate, refers to vitamin C, which plays a key role in the antioxidant system by participating in the regenerative processes of other antioxidants, including a specific regeneration mechanism that involves thioredoxin reductase.

Thioredoxin reductase is an essential enzyme that, together with thioredoxin, helps maintain the redox state of the cell by facilitating the reduction of oxidized proteins and assisting in various cellular processes. Ascorbate can donate electrons to oxidized thioredoxin, thus regenerating it back to its active state, allowing the antioxidant system to continue functioning effectively.

While vitamin A, coenzyme Q10, and vitamin E are also important antioxidants, their mechanisms of action do not specifically involve regeneration through thioredoxin reductase in the same way as ascorbate. Vitamin A primarily acts in vision and gene expression, coenzyme Q10 is vital for mitochondrial electron transport and energy production, and vitamin E serves mainly as a lipid antioxidant, protecting cell membranes from oxidative damage. Thus, the specific involvement of ascorbate in the electron transfer processes tied to thioredoxin reductase stands out as the correct answer.