Action spectra determined with tunable dye laser light for light-induced proton efflux and uptake in membrane vesicles of Halobacterium halobium.

A new pigment from Halobacterium halobium has been previously described which mediates the electrogenic extrusion of sodium ions when illuminated. Using essentially monochromatic light (0.05 nm bandwidth), maximum activity for this pigment occurred at 590 nm as monitored by passive proton uptake in envelope vesicles. The uncoupler bis(hexafluoroacetonyl)-acetone did not shift peak activity, but did increase passive proton influx. When the new pigment (NaP590) bacteriorhodopsin, the well characterized proton pump, and were compared at their respective wave-lengths of maximum activity, NaP590 required approximately 100-fold more energy to achieve saturation.