Electrostatic interaction between anions bound to Site I and the retinal Schiff base of halorhodopsin

Journal Article · Tue Jul 01 04:00:00 EDT 1986 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00362a026· OSTI ID:6606119

Schobert, B; Lanyi, J K

The influence of different anions on the deprotonation of the retinal Schiff base of halorhodopsin in the dark was investigated. We find that a large number of anions cause a significant increase of the pK/sub a/ of the Schiff base, an effect attributed to binding to site I on the protein. The concentration dependencies of the spectroscopic shifts associated with the changes of the pK/sub a/ yielded dissociation constants (and thus binding energies) for the anions, which were related to the Stokes radii. The data fit the predictions of electrostatic interaction between the anions and the positive charge associated with site I, if the latter is located within a few angstroms from the surface of the protein. The specificity of site I toward various anions is quantitatively explained by the differences in the change of Born energy upon transfer of the anions from water to the binding site. The changes in the deprotonation energy of the Schiff base upon the binding of anions, ..delta delta..G/sub deprot/, could be calculated from the ..delta..pK/sub a/ at infinite anion concentration. Unexpectedly, the ..delta delta..G/sub deprot/ values were remarkably close to the energies of binding to site I. Thus, site I and the Schiff base are strongly electrostatically coupled, either because of close proximity or because of the possibility of allosteric energy transfer between them.

• Research Organization: Univ. of California, Irvine (USA)
• OSTI ID: 6606119
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 25:13; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ANIONS
BACTERIA
BIOCHEMICAL REACTION KINETICS
CHARGED PARTICLES
ELECTROSTATICS
IONS
KINETICS
MICROORGANISMS
ORGANIC COMPOUNDS
PIGMENTS
PROTEINS
REACTION KINETICS
RHODOPSIN