ABSTRACT
Manganese is a trace element that is essential for both plants and animals. Present at low levels in all human tissues but at generally higher concentrations in tissues rich in mitochondria, it is a cofactor in a number of enzymatic reactions, notably in oxidative metabolism as well as in vitamin K, DNA, RNA, and protein syntheses (1). In response to excessive and toxic superoxide radicals, which can occur during aerobic metabolism, the mitochondria form Mn superoxide dismutase (MnSOD), representing a major class of SOD metalloenzymes that act to transform superoxide radicals to oxygen and hydrogen peroxide (2). When induced by ionizing radiation and hyperoxia, MnSOD is more effective than the corresponding CuZnSOD by virtue of the fact that its half-life in serum is on the order of 5-6 hr (compared to the 6-19 min found for the latter) (3,4).
