Salivary peroxidase: an important part of our defense against oxygen toxicity

All living cells convert dioxygen (O2) into the toxic intermediates of oxygen reduction: superoxide radicals, hydrogen peroxide and hydroxyl radicals. The defense against these intermediates works on three levels: 1) the formation of the intermediates is prevented; 2) the intermediates are scavenged; 3) the damaged sites are repaired. Various parts of this defense are found intracellularly, in tissue fluid, in blood plasma and in the external secretions. In the mouth there is a special need for defense against hydrogen peroxide, because hydrogen peroxide is not only formed by bacteria colonizing the mucous membranes but also by the cells of the salivary glands. In saliva the most important part of this defense is salivary peroxidase, which detoxifies hydrogen peroxide in the presence of thiocyanate by converting it into hypothiocyanite, dioxygen and water. In addition, hypothiocyanite stops hydrogen peroxide production by the oral bacteria.