Related Experiment Video
Updated: Feb 16, 2026

Ammonia Synthesis at Low Pressure
Published on: August 23, 2017
Structural Effects of Ammonia Binding to the Mn4CaO5 Cluster of Photosystem II
David A Marchiori1, Paul H Oyala1,2, Richard J Debus3
1Department of Chemistry, University of California, Davis , Davis, California 95616, United States.
Abstract:
The Mn4CaO5 oxygen-evolving complex (OEC) of photosystem II catalyzes the light-driven oxidation of two substrate waters to molecular oxygen. ELDOR-detected NMR along with computational studies indicated that ammonia, a substrate analogue, binds as a terminal ligand to the Mn4A ion trans to the O5 μ4 oxido bridge. Results from electron spin echo envelope modulation (ESEEM) spectroscopy confirmed this and showed that ammonia hydrogen bonds to the carboxylate side chain of D1-Asp61. Here we further probe the environment of OEC with an emphasis on the proximity of exchangeable protons, comparing ammonia-bound and unbound forms. Our ESEEM and electron nuclear double resonance (ENDOR) results indicate that ammonia substitutes for the W1 terminal water ligand without significantly altering the electronic structure of the OEC.
Related Concept Videos
Photosystem I
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
Photosystem II
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment...
Photosystems
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment...
Conserved Binding Sites
Binding sites are often located in large pockets, and if their location on a protein’s surface is unknown, it can be predicted using various approaches. The energetic method computationally...
The Equilibrium Binding Constant and Binding Strength
Ligand Binding and Linkage

