PROPERTIES OF THE CHLOROPLAST FILM ELECTRODE IMMOBILIZED ON AN SnO2‐COATED GLASS PLATE

Type C chloroplasts were deposited on the surface of an SnO2 optically transparent electrode glass plate with polyvinyl alcohol plus bovine serum albumin as immobilizing supports. This electrode, on illumination of 250 J/m2 in an electrolyte solution, generated anodic photo current more than 150 nA per 10 μg chlorophyll/cm2 of the SnO2 glass plate at a potentiostatic condition of + 0.5 V against a saturated calomel electrode, and gave rise to an open circuit potential up to 300 mV. The photocurrent output was enhanced as high as 60‐fold under the short circuit condition by the addition of an artificial electron carrier, l‐methoxy‐5‐methylphenazinium methyl sulfate, to the electrolyte solution. With the electrode poised at +0.5 V against a saturated calomel electrode, the enhancement effect was exhibited as high as 13‐fold in the presence of 2,6‐dichlorophenol indophenol. A photocurrent spectrum coincides well with an absorption spectrum of the chloroplast film electrode. Effects of heat‐treatment, photosynthetic inhibitors, and electrolyte's pH on the magnitude of the photocurrent were studied in detail. Water molecule, a primary electron donor in the chloroplast photosystems, contributes to the large majority of photocurrent generation. A minor output was observed with the electrode coated with completely inactivated chloroplasts, probably due to the chlorophyll photosensitization.