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XB-ART-318
Biophys J 2006 Aug 15;914:1471-9. doi: 10.1529/biophysj.106.086421.
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H+ -pumping rhodopsin from the marine alga Acetabularia.

Tsunoda SP , Ewers D , Gazzarrini S , Moroni A , Gradmann D , Hegemann P .


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An opsin-encoding cDNA was cloned from the marine alga Acetabularia acetabulum. The cDNA was expressed in Xenopus oocytes into functional Acetabularia rhodopsin (AR) mediating H+ carried outward photocurrents of up to 1.2 microA with an action spectrum maximum at 518 nm (AR518). AR is the first ion-pumping rhodopsin found in a plant organism. Steady-state photocurrents of AR are always positive and rise sigmoidally from negative to positive transmembrane voltages. Numerous kinetic details (amplitudes and time constants), including voltage-dependent recovery of the dark state after light-off, are documented with respect to their sensitivities to light, internal and external pH, and the transmembrane voltage. The results are analyzed by enzyme kinetic formalisms using a simplified version of the known photocycle of bacteriorhodopsin (BR). Blue-light causes a shunt of the photocycle under H+ reuptake from the extracellular side. Similarities and differences of AR with BR are pointed out. This detailed electrophysiological characterization highlights voltage dependencies in catalytic membrane processes of this eukaryotic, H+ -pumping rhodopsin and of microbial-type rhodopsins in general.

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Species referenced: Xenopus
Genes referenced: rho uqcc6

References [+] :
Bieszke, A eukaryotic protein, NOP-1, binds retinal to form an archaeal rhodopsin-like photochemically reactive pigment. 1999, Pubmed