Complete restoration of electron flow from P700 to FA/FB was achieved by incubating a P700 and Fx-containing photosystem (PS) I core protein from Synechococcus sp. 6301 with the 8.9 kDa, FA/FB polypeptide from spinach. The ESR spectrum of the reconstituted PS I complex shows nearly equal photochemical reduction of FA and FB when frozen in darkness and illuminated at 16 K. When illuminated during freezing, both FA and FB are quantitatively reduced and the spectrum is nearly indistinguishable from FA and FB in the control PS I complex. In the reconstituted PS I complex Fx is photochemically reduced only in the presence of F-A and F-B, and the high-field resonance appears indistinguishable from Fx in the control PS I complex. Optical flash photolysis after extensive washing confirms the complete restoration of the P700+ [FA/FBI-back-reaction, indicating quantitative rebinding of the 8.9 kDA polypeptide. This procedure represents the first reconstitution of the PS I complex from a purified PS I core protein and an isolated 8.9 kDa, FA/FB polypeptide, and makes possible independent manipulation of the two subunits that carry the entire electron acceptor system of PS I.
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology
- Cell Biology