title: Charge recombination between P700+ and A1- occurs directly to the ground state of P700 in a photosystem I core devoid of FX, FB, and FA.
abstract: The charge recombination between P700+ and electron acceptor A1- was studied by flash kinetic spectroscopy in a photosystem I core devoid of iron-sulfur centers FX, FB, and FA. We showed previously that the majority of the flash-induced absorption change at 820 nm decayed with a 10-microseconds half-time, which we assigned to the disappearance of the P700 triplet formed from the backreaction of P700+ with A1- [Warren, P.V., Parrett, K.G., Warden, J.T., & Golbeck, J.H. (1990) Biochemistry 29, 6545-6550]. We have reinvestigated this assignment in the near-UV, blue, and near-IR wavelength regions. The difference spectrum from 380 to 480 nm and from 720 to 910 nm shows that the P700+ A1- charge recombination is dominated by the P700 cation rather than the P700 triplet. Accordingly, the 10-microseconds kinetic transient represents the direct backreaction of P700+ with A1-, which repopulates the ground state of P700. This is unlike a P700-FA/FB complex where, in the presence of reduced FX-, FB-, and FA-, the P700+ A1- charge recombination populates the P700 triplet state [Sétif, P., & Bottin, H. (1989) Biochemistry 28, 2689-2697]. The A1 acceptor is highly susceptible to disruption by detergents in the absence of iron-sulfur center FX. The addition of 0.1% Triton X-100 to the P700-A1 core leads to a approximately 2.5-fold increase in the magnitude of the flash-induced absorption change at 780 nm; thereafter, 85% of the absorption change decays with a 25-ns half-time and 15% decays with a 3-microseconds half-time.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, University of Nebraska, Lincoln 68583-0718.
authors.forename: P V
authors.initials: PV
authors.lastname: Warren
authors.forename: J H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: J T
authors.initials: JT
authors.lastname: Warden
mesh_terms: D004734:Energy Metabolism; D007506:Iron-Sulfur Proteins / Q000172:deficiency*; D007700:Kinetics; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects; D045331:Photosystem I Protein Complex; D010944:Plants / Q000378:metabolism*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D007506:Iron-Sulfur Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex