Glutathione peroxidase contains selenium as a prosthetic group. In erythrocytes and other tissues, it catalyses the destruction of hydrogen peroxide and lipid peroxidase, protecting membrane lipids and hemoglobin against oxidation. Must know: Some other Co-factors that have been asked: Cofactor for carbonic anhydrase: Zn Cofactor for tyrosinase: Cu Cofactor for cytochrome oxidase Cu Cofactor for xanthine oxidase: Mo Cofactor for transamination reaction: Pyridoxine Cofactor for superoxide dismutase: Mn Ref: Bender D.A., Mayes P.A. (2011). Chapter 21. The Pentose Phosphate Pathway & Other Pathways of Hexose Metabolism. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.