Action of Heavy Metals on Hill Activity and O₂ Evolution in Anacystis nidulans

Addition of 5 micromolar Cu(2+), Cd(2+), and Zn(2+) was inhibitory to 10 micromolar H(2)O(2)-supported Hill activity (dichlorophenolindophenol reduction) and O(2) evolution in membrane preparation from Anacystis nidulans. The reversal of Cd(2+) and Zn(2+) inhibition, in contrast to Cu(2+), by exogenously added catalase (EC 1.11.1.6) suggested that the former cations were inhibitory to H(2)O(2) degradation. Ascorbic acid (20 micromolar) supported 27% of the Hill activity which was insensitive to DCMU (10 micromolar) and the remaining activity, attributable to the DCMU sensitive process, was sensitive to inhibition by Cu(2+) only. It is suggestive that the action site of Cd(2+) and Zn(2+) is located between the electron donation sites of H(2)O(2) and ascorbic acid, while that of Cu(2+) is located beyond it. Electron donation by reduced glutathione was insensitive to DCMU and Cu(2+), indicating that the action site of Cu(2+) is prior to its electron donation site. Further, the phenanthroline (10 micromolar) reversal of Cu(2+) inhibition of Hill activity suggested a tentative action site of Cu(2+) at the level of cytochrome.