Lipid-Controlled Stabilization of Charge-Separated States (P + Q B - ) and Photocurrent Generation Activity of a Light-Harvesting-Reaction Center Core Complex (LH1-RC) from Rhodopseudomonas palustris.

The photosynthetic light-harvesting-reaction center core complex (LH1-RC) is a natural excitonic and photovoltaic device embedded in a lipid membrane. In order to apply LH1-RCs as a biohybrid energy-producing material, some important issues must be addressed, including how to make LH1-RCs function as efficiently as possible. In addition, they should be characterized to evaluate how many active LH1-RCs efficiently work in artificial systems. We report here that an anionic phospholipid, phosphatidylglycerol (PG), stabilizes the charge-separated state (a photooxidized electron donor and reduced quinone pair, P ⁺ Q _B ^- ) of LH1-RC (from Rhodopseudomonas palustris) and enhances its activity in photocurrent generation. Steady-state fluorometric analysis demonstrated that PG enhances the formation of the P ⁺ Q _B ^- state at lower irradiances. The photocurrent generation activity was analyzed via Michaelis-Menten kinetics, revealing that 38% of LH1-RCs reconstituted into the PG membrane generated photocurrent at a turnover frequency of 46 s ^-1 . PG molecules, which interact with LH1-RC in vivo, play the role of an active effector component for LH1-RC to enhance its function in the biohybrid system.