Mössbauer Studies of Cu(II) Ions Interaction with the Non-Heme Iron and Cytochrome b₅₅₉in a Chlamydomonas reinhardtii PSI Minus Mutant

Mssbauer spectroscopy was applied, for the first time, to study the interaction of copper ions with the non-heme iron and the heme iron of cytochrome b559 in photosystem II thylakoids isolated from a Chlamydomonas reinhardtii photosystem I minus mutant. We showed that copper ions oxidize the heme iron and change its low spin state into a high spin state. This is probably due to deprotonation of the histidine coordinating the heme. We also found that copper preserves the non-heme iron in a low spin ferrous state, enhancing the covalence of iron bonds as compared to the untreated sample. We suggest that a disruption of hydrogen bonds stabilizing the quinone-iron complex by Cu 2+ is the mechanism responsible for a new arrangement of the binding site of the non-heme iron leading to its more "tense" structure. Such a diamagnetic state of the non-heme iron induced by copper results in a magnetic decoupling of iron from the primary quinone acceptor. These results indicate that Cu does not cause removal of the non--heme iron from its binding site. The observed Cu 2+ action on the non--heme iron and cytochrome b 559 is similar to that previously observed for -tocopherol quinone.