Properties and photochemistry of a halorhodopsin from the haloalkalophile, Natronobacterium pharaonis.

摘要: Pharaonis halorhodopsin is a light-driven transport system for chloride, similarly to the previously described halorhodopsin, but we find that it transports nitrate as effectively chloride. We studied photoreactions of purified, detergent-solubilized pharaonis pigment with gated multichannel analyzer. At physiological salt concentration (4 M NaCl), absorption spectra and rate constants rise decay intermediates photocycle were similar those halorhodopsin. In buffer containing nitrate, exhibits second, truncated photocycle; this difference in photoreaction occurs when an anion bound such way preclude transport. As expected from lack specificity transport, was nearly unaffected by replacement chloride nitrate. All presumed buried positively charged residues, which might play role binding, are conserved two pigments. extracellular end helix C, however, arginine residue found not arginine-rich segment between helices A B replaced less sequence (Lanyi, J. K., Duschl, A., Hatfield, G. W., May, Oesterhelt, D. (1990) Biol. Chem. 265, 1253-1260). One or both these alterations may explain selectivity proteins.