HMOX1 and Hypertension: Heme is a prosthetic group for fundamental proteins such as hemoglobin, myoglobin, cytochromes, HO-1, catalases, or peroxidases, in addition to important enzymatic systems in hypertension, such as COX or NOS (Kumar and Bandyopadhyay, 2005; Loboda et al., 2008); however, heme can also be harmful once released from hemoproteins.