A group of enzymes which remove hydrogen peroxide (H2O2) from the cell by turning it into water. Hydrogen peroxide is a very harmful radical that, if left alone, will cause extensive damage to DNA. These enzymes are thus very important to all living things which use oxygen (aerobes) because the use of oxygen in respiration often results in the formation of hydrogen peroxide as a waste product. (The formation of hydrogen peroxide is also a major reason why obligate anaerobes find oxygen to be a poison.)