Generation of cathodic photocurrent by photosynthetic reaction center complexes from Rhodospirillum rubrum at a Pt electrode

A platinum electrode immersed in a photosynthetic reaction center suspension, which was prepared from a photosynthetic bacterium, Rhodospirillum rubrum, brought about, on illumination, a cathodic photocurrent under potentiostatic conditions. The photocurrent increased with the increase in cathodic potential up to about -500 mV vs. NHE, The photocurrent also depended on density of the reaction center suspension and on intensity of the incident light. The photocurrent action spectrum coincided fairly well with the absorption one of the reaction center suspension, exhibiting maxima at 600, 800 and 850 nm. The photocurrent was largely enhanced by the addition of 1-methoxy-5-methyl-phenazinium methyl sulfate (methoxy-PMS) to the suspension. The mechanism for the generation of the photocurrent and the role of methoxy-PMS in generating of the photocurrent are discussed.