Takaya Matsukawa

Electron paramagnetic resonance study of the magnetic structure of the S1-state in oriented oxygen evolving photosystem II membranes

Abstract The S 1 -state of the oxygen evolving complex was studied in oriented photosystem II membranes by parallel polarization electron paramagnetic resonance (EPR) spectroscopy. The EPR intensity, ascribed to the S 1 -state Mn-cluster with S =1, varies depending on the magnetic field direction relative to the membrane normal: maximum and minimum were observed at angles of 0 and 90°, respectively. Successful simulations of line shape and intensity observed in the non-oriented and the oriented membranes were obtained using the values of the zero-field parameter, D =±0.14±0.01 cm −1 and E / D =−0.11±0.02, by assuming an isotropic g -value of 2.0. The anisotropy in EPR intensity shows that the axial direction of the zero-field interaction of the manganese cluster is almost parallel to the membrane plane.

Magnetic Susceptibility of the Non-Heme Iron in Photosystem II

The magnetic susceptibility of the non-heme iron in plant photosystem II was first measured by a highly sensitive magnetometer equipped with a pulsed magnetic field. From the temperature dependence of the paramagnetic susceptibility of the non-heme ferrous iron with S =2, the zero-field interaction parameters D and E were determined to be 5.5±1.0 and 0.75±0.75 cm -1 , respectively. These values are almost the same as those observed in a purple photosynthetic bacterium Rhodobacter sphaeroides , suggesting that the structure of the acceptor side of plant photosystem II is also similar to that of the purple photosynthetic bacterium.

Dual Mode EPR Study of S 3 -State Manganese Cluster in the Oxygen Evolving Photosystem II

The function of oxygen evolution is known to be catalyzed by a manganese cluster located on the donor side of PS II. Successive abstraction of four electrons from oxygen evolving center was carried out by four times absorption of light by P680 and results in evolution of molecular oxygen. The oxidizing center cycles through a series of the five oxidation states, called S-states with Sn (n = 0 to 4), n denoting the number of stored oxidizing equivalents. The S4-state is a transient state because it rapidly decays to the S0-state by releasing molecular oxygen. The S1-state is most stable of five oxidation states in dark at room temperature. The S2- and S3-states are unstable and decay back to the S1-state. (1, 2)