H+ -pumping rhodopsin from the marine alga Acetabularia

Biophys J. 2006 Aug 15;91(4):1471-9. doi: 10.1529/biophysj.106.086421. Epub 2006 May 26.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetabularia / physiology*
  • Acetabularia / radiation effects
  • Dose-Response Relationship, Radiation
  • Light
  • Marine Biology
  • Membrane Potentials / physiology*
  • Membrane Potentials / radiation effects
  • Proton Pumps / physiology*
  • Proton Pumps / radiation effects
  • Radiation Dosage
  • Rhodopsin / physiology*
  • Rhodopsin / radiation effects
  • Seawater / microbiology


  • Proton Pumps
  • Rhodopsin