Fig. 7.

Regulation of myocardial mitochondrial topoisomerase activity. A: H₂O₂ increases mitochondrial topoisomerase-dependent DNA cleavage. Mitochondria were preincubated in the absence or presence of 60 μM H₂O₂ prior to the addition of DNA. *P < 0.05 compared with respective no mitochondria/H₂O control; #P < .0.05 compared with +mitochondria/H₂O. B: dephosphorylation alters mitochondrial topoisomerase DNA cleavage activity. No Mito: no extract; +Mito: untreated mitochondria; CIP trt, mitochondria treated with 1 U calf intestinal phosphatase for 30 min at 37°C before DNA was added. Values are means ± SE and are normalized to no Mito or no Mito/H₂O; *P < 0.05 compared with No Mito; #P < 0.05 compared with untreated mitochondria.