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 µA 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 trans-membrane 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 trans-membrane 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 eucaryotic, H+ pumping rhodopsin and of microbial-type rhodopsins in general.
|Titolo:||H+ pumping rhodopsin from the marine alga Acetabularia|
|Parole Chiave:||Xenopus oocytes ; bacteriorhodopsin ; electrophysiology ; enzyme kinetics ; rhodopsin photocurrents|
|Settore Scientifico Disciplinare:||Settore BIO/04 - Fisiologia Vegetale|
|Data di pubblicazione:||2006|
|Digital Object Identifier (DOI):||10.1529/biophysj.106.086421|
|Appare nelle tipologie:||01 - Articolo su periodico|