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Photosystem I (PSI) is a photoactive electron-transport protein found in plants that participates in the process of photosynthesis. Because of PSI's abundance in nature and its efficiency with charge transfer and separation, there is a great interest in applying the protein in photoactive electrodes. Here, we developed a completely organic, transparent, conductive electrode using reduced graphene oxide (RGO) on which a multilayer of PSI could be deposited. The resulting photoactive electrode demonstrated current densities comparable to that of a gold electrode modified with a multilayer film of PSI and significantly higher than that of a graphene electrode modified with a monolayer film of PSI. The relatively large photocurrents produced by integrating PSI with RGO and using an opaque, organic mediator can be applied to the facile production of more economic solar energy conversion devices.
Photosystem I (PSI) is a membrane protein complex that generates photoinduced electrons and transfers them across the thylakoid membrane during photosynthesis. The PSI complex, separated from spinach leaves, was spread onto the air-water interface as a monolayer and transferred onto a gold electrode surface that was precoated with a self-assembled monolayer (SAM). The electrochemical properties of the transferred PSI monolayer, including cyclic voltammetry and photoinduced chronoamperometry, were measured. The results showed that PSI retained its bioactivity after the manipulation. Its capability of converting photoenergy into electrical potential was demonstrated by its reducing an electron acceptor, dichloroindophenol (DCIP), and by oxidizing an electron donor, sodium ascorbate (ASC). We have shown that the protein has two possible orientations at the water interface. The orientation distribution was determined by comparing the controlled reductive and oxidative photocurrents generated from Langmuir-Blodgett and Langmuir-Schaefer monolayers.
Monoamines, including both dopamine and serotonin, synapse onto prefrontal cortical interneurons. Dopamine has been shown to activate these GABAergic interneurons, but there are no direct data on the effects of serotonin on GABA release in the prefrontal cortex. We, therefore, examined the effects of the 5-HT2a/c agonist 1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI) on extracellular GABA levels in the prefrontal cortex of the rat. Local infusions of DOI dose-dependently increased cortical extracellular GABA levels. In addition, systemic DOI administration resulted in Fos protein expression in glutamic acid decarboxylase67-immunoreactive interneurons of the prefrontal cortex. These data indicate that serotonin, operating through a 5-HT2 receptor, acutely activates GABAergic interneurons in the prefrontal cortex. These data further suggest that there may be convergent regulation of interneurons by dopamine and serotonin in the prefrontal cortex.