Ferrochelatase activity in normal and irradiated animal tissues.

Abstract

Ferrochelatase activity is present in rat and mouse liver, heart, kidney, spleen, bone marrow and intestinal mucosa. Enzyme activity is concentrated in the mitochondrial fraction and absent from the microsomal fraction. About 20% of the total activity of liver is in the 100,000 ×g supernatant. Formation of lipid peroxides in mitochondria leads to some loss of enzyme activity but extensive lipid peroxidation can occur without substantial reduction in enzyme activity. Ferrochelatase in tissue homogenates, mitochondria or in a purified form is unaffected by 50 kilorads in vitro but is 15%–30% inhibited after keeping irradiated samples for 20 h at 4°. In liver, heart and muscle homogenates the activity of ferrochelatase, in mice irradiated with a whole body dose of 850 rads was not outside the range of control values; but in kidney, spleen, bone marrow and in liver and kidney mitochondria, there was an increase of enzyme activity on the 3rd day after irradiation, followed by a decrease and return to normal on the 9th–10th days. It is considered unlikely that a decline in ferrochelatase activity can account for the accumulations of iron found in tissues of irradiated animals or that it is an important site of radiation damage in vivo.