Abstract— Reaction center (RC) complexes isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides R‐26 were dried as a film onto platinum and semiconductor (SnO2) electrodes. The light‐induced primary charge separation which occurs across the biological complex couples electrically with the SnO2 but not with the metal electrode on the time scale of observation. As the working electrode in a two‐electrode photoelectrochemical cell, RC‐coated SnO2 generated photovoltages as high as 80 mV and photocurrents as high as 0.5µA·cm2 when exposed to light of λ >600nm. The number of quinone molecules per RC strongly influences the photovoltage and photocurrent observed. Photo‐effects generated by RC electrodes persist after several days of storage; however, the kinetics and polarity of the effects are subject to change. The potential use of RC electrodes lies more as a new probe of photosynthetic electron transport rather than as a solar energy conversion device because modification to the RCs and their environment affect the electrical properties of the cell. An energy‐level model is proposed to explain how the photoelectrochemical cell functions.
Measurements were made of energy-dependent quenching of atebrin fluorescence in membrane particles prepared from Escherichia coli grown anaerobically with glycerol as carbon source in the presence of either nitrate or fumarate. It is concluded that this technique can be used to study the functional organization of the anaerobic proton-translocating electron-transport chains that use nitrate or fumarate as terminal electron acceptor.
Corrections to photocount distributions due to dead-thne effects are evaluated by the use of a new pulse-plleup model Incorporating a paralyzable portion and nonparalyzable component In sequence. In the simple model, the two dead times are regarded as nonvarying. A more complete model Is presented In the Appendix, which Incorporates dead times that are themselves random variables.1121 amplifier discriminator and a Model 1109 photon counter) and suggest that the counting system can be considered to be composed of four simplified parts: a detector (including the diode string), an amplifier discriminator, a pulse shaper (within the amplifier discriminator), and a counter. We propose that the detector and amplifier discriminator are both paralyzable systems and can be represented by a single rate-limiting paralyzable counting mechanism. The pulse shaper and counter have electronic components that are nonparalyzable and slower than the previous circuits. They can be represented by a single, rate-limiting nonparalyzable mechanism. The pulse-pileup effects can then be derived for the two sequential systems, each with its own dead time (see also ref 6).
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