RECONSTITUTION OF THE PHOTOSYSTEM-I SECONDARY QUINONE ACCEPTOR (A(1))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 replac ed by the 25 ns decay, which was interpreted as the backreaction occur ring in a P700+-A0- pair in place of a P700+-F(X)- pair. When phylloqu inone was added to the phylloquinone-depleted core, the 1 ms decay of P700+ was recovered only in a concomitant presence of Triton X-100. Th e 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 n ot eliminate the effects of phylloquinone, suggesting that the reconst ituted phylloquinone was as tightly bound to the P700-F(X) core as is the naturally-occurring A1.