Light-driven chloride ion transport by halorhodopsin from Natronobacterium pharaonis: 1. The photochemical cycle

Journal Article · Tue Nov 07 04:00:00 EST 1995 · Biochemistry (Eaton)

DOI:https://doi.org/10.1021/bi00044a027· OSTI ID:415158

Varo, G; Brown, L S; Sasaki, J ^[1]

---

1. Univ. of California, Irvine, CA (United States)

The photochemical cycle of the light-driven chloride pump, halorhodopsin from N. pharonis, is described by transient optical multichannel and single-wavelength spectroscopy in the visible, and in the infrared. Titration of a blue-shift of the adsorption maximum upon addition of chloride describes a binding site with a K{sub D} of 1 mM. The reaction sequence after the all-trans to 13-cis photoisomerization of the retinal in this chloride binding form is itself dependent on the chloride. At 2 M chloride it is described by the scheme: HR {yields} K {leftrightarrow} L {leftrightarrow} N {yields} HR that relaxes in a few milliseconds, and is very similar to the photocycle of bacteriorhodopsin under conditions where the retinal Schiff base cannot deprotonate. At lower chloride concentrations, e.g., 0.1 M, however, a red-shifted state termed O appears between N and HR, in equilibrium with N. The absorption spectra of K, L, N, and O are very similiar to their counterparts in the bacteriorhodopsin photocycle. As in their equivalents in bacteriorhodopsin, in the N state the retinal is still 13-cis, but it is reisomerized in the O state to all-trans. 90 refs., 8 figs., 1 tab.

• Sponsoring Organization: USDOE
• DOE Contract Number: FG03-86ER13525; FG02-92ER20089
• OSTI ID: 415158
• Journal Information: Biochemistry (Eaton), Journal Name: Biochemistry (Eaton) Journal Issue: 44 Vol. 34; ISSN 0006-2960; ISSN BICHAW
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
ABSORPTION SPECTRA
BACTERIA
BIOCHEMISTRY
CHLORIDES
ISOMERIZATION
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
PHOTOCHEMICAL REACTIONS
PROTONS
RHODOPSIN