Protein (tyrosine)-chromophore (protonated Schiff base) coupling in bacteriorhodopsin
The kinetics of formation of both the tyrosinate ion (from its absorption at 296 nm) and the deprotonated Schiff base (M/sub 412/) (from its absorption at 404 nm) are studied simultaneously at different pH values (7-11) and temperatures (5-25/sup 0/C). Two formation rates are observed for M/sub 412/ in agreement with previous observations. The slow one is dominant under physiological conditions and is found to be slightly faster than that for the tyrosinate formation. This is in disagreement with the proposal that the tyrosinate formation is a prerequisite to the deprotonation of the Schiff base (M/sub 412/). The ratio of the amplitudes of the fast and slow components is found to be sensitive to pH and, at any pH, it can be used to calculate an amino acid pK/sub a/ value of 9.6. This is explained by proposing the existence of two sites for the protonated Schiff base within the protein. In one site, the Schiff base is near the neutral form of an amino acid residue with a pK/sub a/ value of 9.6 (giving rise to the slow component), while in the other, it is near its conjugate base. The formation of the tyrosinate ion as well as the formation of the slow and fast components of M/sub 412/ all have activation energies that are comparable to H-bond energies. A model is suggested to account for this and the comparable deprotonation rates of tyrosine and the slow component of the protonated Schiff base. It involves the reduction of their pK/sub a/ by their exposure to a positively charged species. 43 references, 2 figures, 2 tables.
- Research Organization:
- Univ. of California, Los Angeles, CA (United States)
- OSTI ID:
- 5933681
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 81:22
- Country of Publication:
- United States
- Language:
- English
Similar Records
Substitution of amino acids Asp-85, Asp-212, and Arg-82 in bacteriorhodopsin affects the proton release phase of the pump and the pK of the Schiff base
Effects of tyrosine-26 and tyrosine-64 nitration on the photoreactions of bacteriorhodopsin
Related Subjects
RHODOPSIN
BIOCHEMISTRY
BIOCHEMICAL REACTION KINETICS
CELL MEMBRANES
MATHEMATICAL MODELS
PH VALUE
PROTONS
SCHIFF BASES
TEMPERATURE EFFECTS
TYROSINE
AMINO ACIDS
BARYONS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHEMISTRY
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HYDROXY ACIDS
IMINES
KINETICS
MEMBRANES
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PROTEINS
REACTION KINETICS
550200* - Biochemistry