Action of Heavy Metals on Hill Activity and O2 Evolution in Anacystis nidulans1

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RESUMO

Addition of 5 micromolar Cu2+, Cd2+, and Zn2+ was inhibitory to 10 micromolar H2O2-supported Hill activity (dichlorophenolindophenol reduction) and O2 evolution in membrane preparation from Anacystis nidulans. The reversal of Cd2+ and Zn2+ inhibition, in contrast to Cu2+, by exogenously added catalase (EC 1.11.1.6) suggested that the former cations were inhibitory to H2O2 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 Cu2+ only. It is suggestive that the action site of Cd2+ and Zn2+ is located between the electron donation sites of H2O2 and ascorbic acid, while that of Cu2+ is located beyond it. Electron donation by reduced glutathione was insensitive to DCMU and Cu2+, indicating that the action site of Cu2+ is prior to its electron donation site. Further, the phenanthroline (10 micromolar) reversal of Cu2+ inhibition of Hill activity suggested a tentative action site of Cu2+ at the level of cytochrome.

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