Reconstitution and immobilization of photo-reaction units from photosynthetic bacterium Rhodopseudomonas viridis

Photo-reaction units (PRUs) were solubilized from chromatophores of the photosynthetic bacterium Rhodopseudomonas viridis under high salt concentration using Triton X-100 as a detergent. The absorption spectrum of isolated PRUs was similar to that of native chromatophores. Isolated PRUs were composed of reaction centers (RCs) and light-harvesting (LH) proteins. Purified PRUs were reconstituted into liposomes. The QY absorption bands derived from bacteriochlorophyll (BChl) b in LH subunits of PRUs were red-shifted from 1000 nm in the isolated PRUs solution to 1006 nm in the reconstituted liposomes, contrasting with the 1015 nm for native PRUs in chromatophores. To make a photo-electrochemical conversion layer for photocell or biosensor, we deposited PRU liposomes on a solid substrate by electrodeposition. The orientation angle between the molecular axis of PRUs and the disk normal was 2.4° for the deposited PRU liposomes, compared with 20.5° for purified chromatophores deposited. This demonstrates that the vertical alignment of protein molecules with the disk normal was superior for electrodeposited protein molecules immobilized using PRU liposomes compared with those using purified chromatophores.