Photosystem additional studies

Mn(III) complex for the solution represented by curve C. Apparently, the excess K3Fe(CN)6 oxidizes the free ligand in the solution, and this in turn is catalytically reduced by the reduced form of the Mn(III) complex. Because of the presence of quinone-like materials in photosystem II (2), this represents a model that warrants additional study. 

Tetranuclear iron-sulfur clusters are key relay stations in the electron flow in photosynthesis. Photosystem I comprises three subunits, PsaA, PsaB and PsaC. The latter contains two [Fe4S4] centres FA and FB. The core subunits PsaA and B, respectively, house a [Fe4S4] centre denoted FX in addition to other, organic cofactors. The role of this latter cluster was probed in preparations partially devoid of PsaC. It was concluded from the results that FX has a major role in controlling the electron transport through PS I.236 Since the final acceptor of the electrons in PS I is a ferredoxin with a [Fe2S2] cluster it was of interest to study a... 

The reactions of the several manganese gluconate complexes with molecular oxygen and hydrogen peroxide have been studied in terms of stoichiometry and reaction kinetics. Reaction mechanisms are proposed on the basis of the kinetic data. In addition, the thermodynamic and mechanistic characteristics of an ideal model system for photosystem-II are analyzed and evaluated. 

B). Thus, the results based on the data from crystallographic and kinetic studies, combined with the application of the rate-vx.-distance dependency, provide additional support for the electron-transfer sequence FeS-X- FeS-A- FeS-B Fd for the photosystem-1 acceptors. This transfer sequence is illustrated by the schematic drawing ofDiaz-Quintana etal showing the arrangement ofthe iron-sulfur clusters in photosystem 1, as shown on the right. 

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