Biomaterial Database

Photoelectric characterization of forward electron transfer to iron-sulfur centers in photosystem I. 1995

W Leibl, and B Toupance, and J Breton

CEA-Saclay, Département de Biologie Cellulaire et Moléculaire, Gif-sur-Yvette, France.

The photoelectric response of oriented PS I membranes from the cyanobacterium Synechocystis 6803 has been investigated in the nanosecond time range. Besides an unresolved rapidly rising phase, there is a further positive electrogenic phase with a rise time constant of 220 +/- 20 ns. The amplitude of the 220-ns phase is 66 +/- 10% that of the subnanosecond phase. The fast phase contains two kinetic components faster than 100 ps, which have recently been resolved and attributed to primary charge separation (P+Ao-formation) and subsequent electron transfer to A1, respectively (Hecks, B., Wulf, K., Breton, J., Leibl, W., & Trissl, H.-W. (1994) Biochemistry 33, 8619-8624). The 220-ns phase is lost under conditions where iron-sulfur centers FA, FB, and Fx are prereduced, and its kinetics match the reoxidation kinetics of A1- as verified by absorbance change measurements at 380 nm. Therefore, this electrogenic phase is attributed to electron transfer to the iron-sulfur centers that function as further electron acceptors in the PS I reaction center. Gradual removal of FA and FB by urea treatment reveals that the amplitude of the 220-ns phase is linearly correlated with the fraction of FA,B present. However, complete removal of FA,B does not lead to a complete loss of the nanosecond phase but reduces its amplitude by more than a factor of 2 to yield an amplitude of 25-30% relative to the initial picosecond rise, with only a slight change in kinetics. The residual amplitude is further reduced when a large fraction of Fx is removed.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007506	Iron-Sulfur Proteins	A group of proteins possessing only the iron-sulfur complex as the prosthetic group. These proteins participate in all major pathways of electron transport: photosynthesis, respiration, hydroxylation and bacterial hydrogen and nitrogen fixation.	Iron-Sulfur Protein,Iron Sulfur Proteins,Iron Sulfur Protein,Protein, Iron-Sulfur,Proteins, Iron Sulfur,Proteins, Iron-Sulfur,Sulfur Proteins, Iron
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D010777	Photochemistry	A branch of physical chemistry which studies chemical reactions, isomerization and physical behavior that may occur under the influence of visible and/or ultraviolet light.	Photochemistries
D004579	Electron Transport	The process by which ELECTRONS are transported from a reduced substrate to molecular OXYGEN. (From Bennington, Saunders Dictionary and Encyclopedia of Laboratory Medicine and Technology, 1984, p270)	Respiratory Chain,Chain, Respiratory,Chains, Respiratory,Respiratory Chains,Transport, Electron
D000458	Cyanobacteria	A phylum of oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing CHLOROPHYLL a and carrying out oxygenic PHOTOSYNTHESIS. Cyanobacteria are the only known organisms capable of fixing both CARBON DIOXIDE (in the presence of light) and NITROGEN. Cell morphology can include nitrogen-fixing heterocysts and/or resting cells called akinetes. Formerly called blue-green algae, cyanobacteria were traditionally treated as ALGAE.	Algae, Blue-Green,Blue-Green Bacteria,Cyanophyceae,Algae, Blue Green,Bacteria, Blue Green,Bacteria, Blue-Green,Blue Green Algae,Blue Green Bacteria,Blue-Green Algae
D045322	Photosynthetic Reaction Center Complex Proteins	Protein complexes that take part in the process of PHOTOSYNTHESIS. They are located within the THYLAKOID MEMBRANES of plant CHLOROPLASTS and a variety of structures in more primitive organisms. There are two major complexes involved in the photosynthetic process called PHOTOSYSTEM I and PHOTOSYSTEM II.	Photosynthetic Complex,Photosynthetic Reaction Center,Photosynthetic Reaction Center Complex Protein,Photosynthetic Complexes,Photosynthetic Reaction Centers,Center, Photosynthetic Reaction,Complex, Photosynthetic,Complexes, Photosynthetic,Reaction Center, Photosynthetic,Reaction Centers, Photosynthetic