Photoelectric Effects From Chlorophyll A in Bilayer Membranes

Light flashes generated voltage transients across bilayer membranes in air-saturated solutions which had chlorophyll a (Chi a) incorporated from one side. No other membrane or solution asymmetry was required. Symmetrical membranes containing Chi a also produced photovoltages after transmembrane NaCl gradients were established, and large membrane conductance changes when irradiated in the presence of Nal. The latter two effects were reduced when the oxygen tension was reduced, and are consistent with photoionization of Chi a producing porphyrin radicals and superoxide. Other oxidizing agents, CuS04, FeCl3, K3Fe(CN)6, (NH4)2Ce(N03)6 and S-(2-methyl-l,4-naphthquinonyl-3)-gutathione, increased the photoelectric effect's amplitudes when they came into contact with Chi a. The quantum efficiency with 5 mM K3Fe(CN)6 was estimated by the dual flash method to be 0.2 ± 0.1.