Electron spin polarization in photosynthesis and the mechanism of electron transfer in photosystem. I. Experimental observations

Journal Article · Wed Mar 01 00:00:00 EST 1978 · Biophys. J.; (United States)

DOI:https://doi.org/10.1016/S0006-3495(78)85522-2· OSTI ID:6800490

Dismukes, G C; McGuire, A; Blankenship, R; Sauer, K

Transient electron paramagnetic response (EPR) methods are used to examine the spin populations of the light-induced radicals produced in spinach chloroplasts, photosystem I particles, and Chlorella pyrenoidosa. We observe both emission and enhanced absorption within the hyperfine structure of the EPR spectrum of P700/sup +/, the photooxidized reaction-center chlorophyll radical (Signal I). By using flow gradients or magnetic fields to orient the chloroplasts in the Zeeman field, we are able to influence both the magnitude and sign of the spin polarization. Identification of the polarized radical and P700/sup +/ is consistent with the effects of inhibitors, excitation light intensity and wavelength, redox potential, and fractionation of the membranes. The EPR signal of the polarized P700/sup +/ radical displays a 30 percent narrower line width than P700/sup +/ after spin relaxation. This suggests a magnetic interaction between P700/sup +/ and its reduced (paramagnetic) acceptor, which leads to a collapse of the P700/sup +/ hyperfine structure. Narrowing of the spectrum is evident only in the spectrum of polarized P700/sup +/, because prompt electron transfer rapidly separates the radical pair. Evidence of cross-relaxation between the adjacent radicals suggests the existence of an exchange interaction.

• Research Organization: Univ. of California, Berkeley, CA (United States)
• OSTI ID: 6800490
• Journal Information: Biophys. J.; (United States), Vol. 21:3
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
PHOTOSYNTHESIS
BIOCHEMICAL REACTION KINETICS
POLARIZATION
CHLORELLA
CHLOROPLASTS
RADICALS
REDOX POTENTIAL
SPECTRA
SPINACH
ALGAE
BIOMASS
CELL CONSTITUENTS
CHEMICAL REACTIONS
ENERGY SOURCES
FOOD
KINETICS
MAGNETIC RESONANCE
MICROORGANISMS
PHOTOCHEMICAL REACTIONS
PLANTS
REACTION KINETICS
RENEWABLE ENERGY SOURCES
RESONANCE
SYNTHESIS
UNICELLULAR ALGAE
VEGETABLES
550200* - Biochemistry
551000 - Physiological Systems