VECTORIAL PHOTOCURRENTS AND PHOTOCONDUCTIVITY IN METALLIZED CHLOROPLASTS

A novel photobiophysical phenomenon was observed in isolated spinach chloroplasts that were metalized by precipitating colloidal platinum onto the surface of the thylakoid membranes. A two-point irradiation and detection system was constructed in which a continuous-beam helium-neon laser (λ = 632.8 nm) was used to irradiate the platinized chloroplasts at varying perpendicular distances (Figure 1) from a single linear platinum electrode in pressure contact with the platinized chloroplasts. No external voltage bias was applied to the system. The key objective of the experiments reported in this report was to measure the relative photoconductivity of the chloroplast-metal composite matrix. Unlike conventional photosynthetic electrochemical cells, in which irradiated chloroplasts are in close proximity to an electrode or linked to the electrode by an electrode-active mediator, the flow of photocurrent was through the biocomposite material. A sustained steady-state vectorial flow of current in the plane of the entrapped composite from the point of laser irradiation to the wire electrode was measured. The absolute value of the measured photocurrent and the maximum perpendicular distance between the point of irradiation and the linear electrode for which sustained current could be measured depended on the experimental procedure used to prepare the platinized chloroplasts. Figure 2 and Table I summarize the data reported in this report. © 1990 American Chemical Society.