Reconstitution of the photosystem I secondary quinone acceptor (A₁) in the P700-F_x core isolated from synechococcus PCC 6301

By treating a F_A/F_B-depleted P700-F_x core from Synechococcus PCC 6301 with diethylether, most of the phylloquinone was removed without loss of P700. The 1 ms decay of P700⁺ in the original core was replaced by the 25 ns decay, which was interpreted as the backreaction occurring in a P700⁺-A0- pair in place of a P700⁺-Fx- pair. When phylloquinone was added to the phylloquinone-depleted core, the 1 ms decay of P700⁺ was recovered only in a concomitant presence of Triton X-100. The effective concentration of Triton X-100 was between 0.02% and 0.1%. The flash-induced difference spectrum from 400 to 500 nm confirms the participation of F_x in the 1 ms decay of P700⁺ in the reconstituted core. Washing the phylloquinone-reconstituted core with n-hexane did not eliminate the effects of phylloquinone, suggesting that the reconstituted phylloquinone was as tightly bound to the P700-F_x core as is the naturally-occurring A₁.