Effects of tyrosine-26 and tyrosine-64 nitration on the photoreactions of bacteriorhodopsin

Journal Article · Tue Dec 17 00:00:00 EST 1985 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00347a035· OSTI ID:5776463

Scherrer, P; Stoeckenius, W

In the dark, all titratable tyrosine residues of bacteriorhodopsin have pK's of greater than 11.0, which may be caused by the hydrophobic environment for buried residues and by high negative charge density for surface residues (Scherrer, P., and Stoeckenius, W. (1984) Biochemistry 23, 6195-6202). Under illumination, deprotonation of only one tyrosine is observed in the micro- and millisecond time ranges of the photocycle; this is Tyr-64. Nitration of Tyr-64 decreases the chromophore absorbance, shifts the absorption maximum to 535 nm, and affects photocycle kinetics. However, restoring its native pK by reduction after nitration has no effect on the changes in photocycle kinetics or absorbance of the chromophore. Nitration of Tyr-64 apparently causes a conformational change in bR, which is independent of the pK of its phenolic group. These observations contradict earlier conclusions that in the photocycle a tyrosine residue directly interacts with the Schiff base during its deprotonation or reprotonation. The protonation state of Tyr-26 and the alkaline chromophore transition are correlated, as shown earlier (Scherrer and Stoeckenius, 1984). Lowering the pK of Tyr-26 by nitration decreases the M-decay rate, and this effect is partially reversed by reduction of the nitro group. We conclude that Tyr-26 may be located close to the chromophore and interact with it; but its protonation state does not change at physiological pH and in the microsecond time range of the photocycle. Tyr-64 is apparently located at or close to the external surface; its modification strongly affects the chromophore but apparently indirectly and not through its protonation changes.

• Research Organization: Univ. of California, San Francisco
• OSTI ID: 5776463
• Journal Information: Biochemistry; (United States), Vol. 26
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
RHODOPSIN
PHOTOCHEMICAL REACTIONS
AMINO ACID SEQUENCE
BIOCHEMICAL REACTION KINETICS
CAROTENOIDS
EQUILIBRIUM
NITRATES
NITRATION
PHOTOCHEMISTRY
PROTONS
SPECTROPHOTOMETRY
TYROSINE
AMINO ACIDS
BARYONS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HYDROCARBONS
HYDROXY ACIDS
KINETICS
MOLECULAR STRUCTURE
NITROGEN COMPOUNDS
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PIGMENTS
PROTEINS
REACTION KINETICS
TERPENES
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)