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Updated: Jun 2, 2026

Measurement of Total Calcium in Neurons by Electron Probe X-ray Microanalysis
Published on: November 20, 2013
Calcium in the oxygen-evolving complex: structural and mechanistic role determined by X-ray spectroscopy
Vittal K Yachandra1, Junko Yano
1Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. VKYachandra@lbl.gov
Calcium (Ca) is crucial for the photosynthetic water-oxidation reaction. X-ray spectroscopy reveals a MnCa structure, highlighting Ca's essential role in the Mn(4)Ca catalytic center's mechanism.
Area of Science:
- Biochemistry
- Photosynthesis research
- Spectroscopy
Background:
- The photosynthetic water-oxidation reaction is vital for life on Earth.
- Understanding the Mn(4)Ca catalytic center is key to deciphering oxygen evolution.
- The precise role of calcium (Ca) in this process remains an area of active investigation.
Purpose of the Study:
- To review X-ray Absorption Spectroscopy (XAS) studies on the role of Ca in photosynthetic water oxidation.
- To elucidate the structural and mechanistic contributions of Ca within the Mn(4)Ca cluster.
Main Methods:
- X-ray Absorption Spectroscopy (XAS) applied to Photosystem II (PS II) samples.
- Utilizing Ca and Strontium (Sr) substituted PS II for spectroscopic analysis.
- Investigating PS II in various S-states using Sr-substituted samples.
Main Results:
- Established the presence and orientation of a MnCa heteronuclear structure in PS II.
- Demonstrated the requirement of Ca for the catalytic activity of the Mn(4)Ca center.
- Provided insights into Ca's function across different S-states of the catalytic cycle.
Conclusions:
- XAS studies have significantly advanced the understanding of Ca's indispensable role in water oxidation.
- The MnCa heteronuclear structure is a key feature of the water-oxidation catalyst.
- Further research using spectroscopic methods will continue to refine our understanding of this essential biological process.
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