There are two main types of thioredoxin reductase: 1. TrxR1: Found primarily in the cytoplasm and associated with general cellular redox regulation. 2. TrxR2: Located in the mitochondria, playing a critical role in mitochondrial redox balance and energy metabolism. Both types are selenoproteins, containing the rare amino acid selenocysteine in their active sites, which is essential for their catalytic efficiency.
