SUMMARY

Isolated and purified microsomal NADH-cytochrome b5 reduc-tase (EC 1.6.2.2) was incubated with bleomycin (BLM) and FeCl3 in the presence of NADH. Only when purified cytochrome b5 was added could an increased NADH consumption be observed indicating redox cycling of the BLM-Fe(lll) complex. In the pres-ence of DNA, BLM-Fe(lll)-related NADH consumption was ac-companied by malondialdehyde (MDA) formation, further evi-dence for BLM activation yielding oxidative DNA cleavage. BLM, FeCI3, cytochrome b5 and NADH were absolutely necessary to provide these effects. Addition of DNA changed the initial velocity (v0) and the shape of the NADH consumption curves, both probably due to an interaction between DNA and BLM-Fe(llI). Furthermore, DNA effectively protected BLM-Fe(lll) from autoxi-dative degradation during redox cycling. BLM-Fe(lll)-related, re-ductase-catalyzed NADH consumption and MDA formation wer