Mechanisms of Anthracycline-Enhanced Reactive Oxygen Metabolism in Tumor Cells

Table 5

Antioxidant enzyme levels in tumor subcellular fractions. Ehrlich tumor microsomes, mitochondria, and nuclei were prepared and assayed for glutathione peroxidase and SOD activity as described in Materials and Methods. The “cytosol” fraction was the supernatant from the final 65,000 x centrifugation step used in the preparation of the microsomal fraction. Before determination of enzyme activity, the mitochondrial fraction was exposed to ultrasonic disruption on ice with 4 bursts of 15 sec each at 90 watts output to eliminate permeability barriers to appropriate substrates in these assays. The supernatant and pellet resulting from centrifugation of the sonicated mitochondria at 105,000 x and 4°C for 60 min were also assayed from enzyme activities.

Tumor cell fraction	Glutathione peroxidase (nmol/min/mg)	SOD (μg SOD/mg)
Cytosol	(4)^a	(3)
Microsomes	(4)	(3)
Nuclei	(3)	(3)
Mitochondria	(3)	5 (3)
105,000 x supernatant	(3)	(3)
105,000 x pellet	N.D. (3)^b	(3)

^a; numbers in parentheses are numbers of experiments; ^bN.D. is not detectable.