II. Electrical measurements in the nanosecond range of the charge separation from chloroplasts spread at a heptane-water interface. Application of a novel capacitive electrode.

Spinach chloroplasts are spread at a heptane-water interface. Applying a novel capacitative electrode introduced in the preceding paper (Trissl, H.-W. (1980) Biochim. Biophys. Acta 595, 82-95) the changes of the interface potential induced by single laser flashes are investigated. The following results are obtained: (1) The chloroplasts spread at the interface form a thin layer with asymmetrical orientation. The structural state of this layer is discussed. (2) The photovoltage from the interfacial layer shows similar characteristics as the field-indicating absorption change of chloroplast suspensions, the latter reflecting the photosynthetic primary charge separation: (a) Both can be abolished by addition of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea. (b) About one half of the signals can be reactivated by addition of N-methyl-phenazonium methosulfate. (c) Both signals saturate at low flash light intensities. (d) Both signals can be abolished by background illumination of comparable intensities. (e) Both signals are independent of the ionic strength. (3) The half-rise time of the photovoltage is determined to be less than 3 ns. It is suggested from these results that the photovoltage from the interfacial layer reflects the primary charge separation process in photosynthesis, i.e. the latter is accomplished also within less than 3 ns.