Hymenolepis diminuta: Biochemical properties of peroxidase activity in mitochondria

The biochemical properties of a peroxidase previously localized cytochemically in the mitochondria of Hymenolepis diminuta were determined. The method chosen was the o-dianisidine procedure in which the decomposition of hydrogen peroxide has been followed spectrophotometrically. Peroxidase activity was initially demonstrated in the mitochondrial pellet. Subsequently, mitochondrial pellets were sonicated and the membrane and supernatant fractions were tested for peroxidase activity. Enzyme activity was demonstrated in the membrane fraction. The enzyme displayed a pH optimum of 5.0, was ascorbate sensitive, and was inhibited by excess H₂O₂. Neither peroxidase nor catalase were observed in any other fraction of the tapeworm tissue, confirming previous cytochemical investigations.