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Molecular interference of Cd(2+) with Photosystem II
Kajsa G V Sigfridsson1, Gábor Bernát, Fikret Mamedov
1Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
Biochimica Et Biophysica Acta
|October 30, 2004
Summary
Cadmium (Cd2+) inhibits photosynthesis by binding to multiple sites in Photosystem II (PSII), affecting electron transfer and oxygen evolution. These findings reveal new mechanisms of heavy metal toxicity in plants.
Area of Science:
- Biochemistry
- Photosynthesis Research
- Environmental Toxicology
Background:
- Heavy metals, such as cadmium (Cd2+), are known to disrupt electron transfer reactions in Photosystem II (PSII).
- Cd2+ can displace the calcium (Ca2+) cofactor in the Ca/Mn cluster, inhibiting oxygen evolution.
- Cd2+ may also bind to other sites in PSII, potentially affecting proton channels.
Purpose of the Study:
- To investigate the effects of Cd2+ binding to low-affinity sites in PSII.
- To elucidate the impact of Cd2+ on various electron transfer reactions within PSII.
- To understand the mechanisms of Cd2+ inhibition on photosynthetic oxygen evolution.
Main Methods:
- Electron paramagnetic resonance (EPR) spectroscopy of individual redox components.
- Flash-induced variable fluorescence measurements.
- Steady-state oxygen evolution assays.
Main Results:
- Inhibition of electron transfer from Y(Z) to P(680)+, evidenced by loss of flash-induced variable fluorescence.
- Slowing of electron transfer from QA- to QB.
- Inhibition of oxygen evolution through both high- and low-affinity Cd2+ binding sites.
Conclusions:
- Cd2+ exerts inhibitory effects on PSII through multiple binding sites, impacting both high- and low-affinity interactions.
- The binding of Cd2+ disrupts critical electron transfer steps and oxygen evolution.
- Further research is needed to fully characterize the nature and implications of these Cd2+ binding sites.