| Abstract: | Kinetic, circular dichroism, and NADH and NADPH fluorescence quenching studies indicate that these compounds interact with the antimalarial drug primaquine (PQ). The affinity of both pyridine nucleotides for PQ is similar. The data are in contrast with a previous report (Thornalley et al. (1983) Biochem. Pharmacol. 32, 3571-3575) suggesting specificity for the interaction with NADPH. The complex was seen to facilitate electron transfer from NAD(P)H to oxygen, generating oxygen-free radicals which were detected by the spin-trapping technique and to flavin nucleotides, giving rise to flavin semiquinone radicals which were demonstrated by direct ESR spectroscopy under anaerobic conditions. A twofold increase in oxygen uptake and hydroxyl radical generation by the NAD(P)H-PQ complex was observed in the presence of hemoglobin. This effect was independent of heme concentration (in the range 1 X 10(-5)-1 X 10(-4) M) and oxidation state of the iron. Under anaerobic conditions, the NAD(P)H-PQ complex reduces Fe-III to Fe-II hemoglobin, and under aerobic conditions about 65% of the heme chromophore is irreversibly destroyed. Superoxide dismutase inhibits hydroxyl radical generation by the NAD(P)H-PQ pair; this effect is not observed in the presence of hemoglobin. In the presence of microsomes there is a 10-fold increase in both oxygen consumption and hydroxyl radical generation by the NAD(P)H-PQ pair. The fact that both pyridine nucleotides are active, and the inability of SKF 525A in decreasing hydroxyl radical generation, suggests that microsomal reductases are involved in the catalysis. |
