Light harvesting, energy transfer and electron cycling of a native photosynthetic membrane adsorbed onto a gold surface

Abstract

Photosynthetic membranes comprise a network of light harvesting and reaction center pigment-protein complexes responsible for the primary photoconversion reactions: light absorption, energy transfer and electron cycling. The structural organization of membranes of the purple bacterial species Rb. sphaeroides has been elucidated in most detail by means of polarized light spectroscopy and atomic force microscopy. Here we report a functional characterization of native and untreated membranes of the same species adsorbed onto a gold surface. Employing fluorescence confocal spectroscopy and light-induced electrochemistry we show that adsorbed membranes maintain their energy and electron transferring functionality. Gold-adsorbed membranes are shown to generate a steady high photocurrent of 10 microA/cm(2) for several minutes and to maintain activity for up to three days while continuously illuminated. The surface-adsorbed membranes exhibit a remarkable functionality under aerobic conditions, even when exposed to light intensities well above that of direct solar irradiation. The component at the interface of light harvesting and electron cycling, the LH1 complex, displays exceptional stability, likely contributing to the robustness of the membranes. Peripheral light harvesting LH2 complexes show a light intensity dependent decoupling from photoconversion. LH2 can act as a reversible switch at low-light, an increased emitter at medium light and photobleaches at high light.

Jumping Mode Atomic Force Microscopy on Grana Membranes from Spinach

“…Most likely, this is due to the upper membrane being more loosely attached to the lower membrane, which in turn adheres to the surface. Recently, it has been shown that the primary photosynthetic reactions are maintained on surface-adhered membranes (40); here, we found that proteins can reorganize on a large-scale within a membrane despite adhesion to a surface.…”

Bacterial Reaction Centers Purified with Styrene Maleic Acid Copolymer Retain Native Membrane Functional Properties and Display Enhanced Stability

“…Intact photosynthetic membranes have been considered as a more stable alternative to detergentpurified proteins for the generation of photocurrents. [24] Our results indicate that the use of nanodiscs may provide the best of both worlds by offering a protective membrane-like environment that is less prone to membrane damage. Under long-term storage at room temperature (20-25 8C) in the dark, membrane-embedded RCs showed complete degradation after 21 days and LDAO RCs after 100 days (Figure 5 B).…”

Plasmon‐Enhanced Photocurrent of Photosynthetic Pigment Proteins on Nanoporous Silver

“…[16][17][18] Inherent limitations in these systems for achieving high photocurrent magnitudes include low protein loading and light absorption. To address these issues, we have interfaced the RC-LH1 complexes with rough silver (RS), a large surface area material used for surface enhanced Raman spectroscopy (SERS) [19,20] and in emerging plasmon-enhanced solar cell technologies.…”