查看文章

Many heavy metals inhibit electron transfer reactions in Photosystem II (PSII). Cd²⁺ is known to exchange, with high affinity in a slow reaction, for the Ca²⁺ cofactor in the Ca/Mn cluster that constitutes the oxygen-evolving center. This results in inhibition of photosynthetic oxygen evolution. There are also indications that Cd²⁺ binds to other sites in PSII, potentially to proton channels in analogy to heavy metal binding in photosynthetic reaction centers from purple bacteria. In search for the effects of Cd²⁺-binding to those sites, we have studied how Cd²⁺ affects electron transfer reactions in PSII after short incubation times and in sites, which interact with Cd²⁺ with low affinity. Overall electron transfer and partial electron transfer were studied by a combination of EPR spectroscopy of individual redox components, flash-induced variable fluorescence and steady state oxygen evolution measurements. Several effects of …