15N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II.
In natural photosynthesis, the two photosystems that operate in series to drive electron transport from water to carbon dioxide are quite similar in structure and function, but operate at widely different potentials. In both systems photochemistry begins by photo-oxidation of a chlorophyll a, but that in photosystem II (PS2) has a 0.7 eV higher midpoint potential than that in photosystem I (PS1), so their electronic structures must be very different. Using reaction centers from (15)N-labeled spinach, these electronic structures are compared by their photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) NMR measurements. The results show that the electron spin distribution in PS1, apart from its known delocalization over 2 chlorophyll molecules, reveals no marked disturbance, whereas the pattern of electron spin density distribution in PS2 is inverted in the oxidized radical state. A model for the donor of PS2 is presented explaining the inversion of electron spin density based on a tilt of the axial histidine toward pyrrole ring IV causing pi-pi overlap of both aromatic systems.
Diller
Anna
A
Gorlaeus Laboratoria, Leiden Institute of Chemistry, Einsteinweg 55, 2300 RA Leiden, The Netherlands.
Roy
Esha
E
Gast
Peter
P
van Gorkom
Hans J
HJ
de Groot
Huub J M
HJ
Glaubitz
Clemens
C
Jeschke
Gunnar
G
Matysik
Jörg
J
Alia
A
A
D000458:Cyanobacteria / Q000201:enzymology; D004583:Electrons; D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary
D009587:Nitrogen Isotopes; D045332:Photosystem II Protein Complex