STUDIES ON REDUCTION OF AZO-LINKAGES IN HUMAN PLACENTAL HOMOGENATES

Investigations of the capacity of human placental tissue to metabolize exogenous substrates revealed a system present in the soluble fraction of placental homogenates which increased the NADPH-dependent reduction of the azo-linkage of neoprontosil. Characterization of the enzyme system involved indicated striking differences in comparison to the azo-reductase system(s) present in hepatic tissues. Activity of the placental system was not affected by additions in vitro of magnesium ion, nicotinamide, NADP or NAD, and was only very slightly inhibited when incubated under atmospheres of pure oxygen of carbon monoxide. Placental azo-linkage reduction was enhanced by addition in vitro of EDTA, reduced glutathione and glucose 6-phosphate. The addition in vitro of flavins resulted in a decreased rate of conversion of neoprontosil to sulfanilamide. Flavin mononucleotide appeared to possess the greatest inhibitory effect. The system was also inhibited by sulfhydryl reagents. Comparisons of specific activities from homogenates of tissue obtained early in the gestational period vs. that obtained at term revealed no statistically significant differences. Studies on the mechanism of increased azo-linkage reduction revealed that an enzymicnonenzymic system involving d-glucose 6-phosphate: NADP oxidoreductase (EC 1.1.1.49) and 6-phospho-d-gluconate: NADP oxidoreductase (EC 1.1.1.44) could account for this increase in azo-linkage reduction. © 1968.