Which of the following is a selenoprotein?

B. Glutathione peroxidase is considered a selenoprotein because it contains selenium in the form of selenocysteine, which is crucial for its enzymatic activity. This enzyme plays an important role in protecting cells from oxidative damage by catalyzing the breakdown of hydrogen peroxide and organic peroxides. The incorporation of selenium allows glutathione peroxidase to effectively neutralize reactive oxygen species, which is vital in various biological processes and in maintaining proper cellular function.

In contrast, albumin, hemoglobin, and insulin do not contain selenium and are not classified as selenoproteins. Albumin is primarily a protein that serves as a carrier for various substances in the blood. Hemoglobin is responsible for transporting oxygen in red blood cells, and insulin is a hormone that regulates glucose levels. Each of these proteins has distinct functions and structural properties that do not involve selenium.