Characterization of a photosystem I core containing P700 and intermediate electron acceptor A1.
A new photosystem I core has been isolated that is devoid of the bound iron-sulfur clusters but preserves electron flow from P700 to the intermediate electron acceptor A1. The particle is prepared by incubation of a Synechococcus sp. PCC 6301 photosystem I core protein (which contains electron acceptors A0, A1, and FX) with 3 M urea and 5 mM K3Fe(CN)6 to oxidatively denature the FX iron-sulfur cluster to the level of zero-valence sulfur. In this apo-FX preparation, over 90% of the flash-induced absorption change at 820 nm decays with a 10-microseconds half-time characteristic of the decay of the P700 triplet state formed from the backreaction of P700+ with an acceptor earlier than FX. Chemical reduction at high pH values with aminoiminomethanesulfinic acid results in kinetics identical with those seen in the P700 chlorophyll a protein prepared with sodium dodecyl sulfate (SDS-CP1, which contains only electron acceptor A0); the flash-induced absorption change decays primarily with a 25-ns half-time characteristic of the backreaction between P700+ and A0-, and the magnitude of the total absorption change is larger than can be accounted for by the P700 content alone. Addition of oxygen results in a reversion to the 10-microseconds kinetic decay component attributed to the decay of the P700 triplet state. At 77 K, the optical transient in the apo-FX preparation decays with a 200-microseconds half-time characteristic of the backreaction between P700+ and A1-.(ABSTRACT TRUNCATED AT 250 WORDS)
Warren
P V
PV
Department of Chemistry, Portland State University, Oregon 97207.
Parrett
K G
KG
Warden
J T
JT
Golbeck
J H
JH
D001426:Bacterial Proteins / Q000302:isolation & purification* / Q000378:metabolism / Q000528:radiation effects; D003080:Cold Temperature; D000458:Cyanobacteria / Q000032:analysis; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins; D013055:Spectrophotometry, Infrared
D001426:Bacterial Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D010100:Oxygen