Relationship of retinal configuration and internal proton transfer at the end of the bacteriorhodopsin photocycle

Journal Article · Tue Dec 03 04:00:00 EST 1996 · Biochemistry (Eaton)

DOI:https://doi.org/10.1021/bi9612430· OSTI ID:569158

Richter, H T; Lanyi, J K ^[1]; Needleman, R ^[2]

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1. Univ. of California, Irvine, CA (United States)
2. Wayne State Univ., Detroit, MI (United States); and others

In the last step of the bacteriorhodopsin photocycle the initial state is regenerated from the O intermediate in an essentially unidirectional reaction. Comparison of the rate of this photocycle step and the rate of deprotonation of Asp-85 in pH jump experiments with various site-specific mutants indicates that recovery of the initial state is influenced by (1) residues such as Glu-204 that affect deprotonation of Asp-85 and (2) residues such as Leu-93 that contact the retinal and therefore must affect its thermal reisomerization from 13-cis to all-trans as suggested by Delaney, Schweiger, and Subramaniam. These results, together with FTIR spectra of the last intermediate in the photocycles of representatives of the two kinds of mutants, E204Q and L93M, suggest the following sequence of events: reisomerization of the retinal from 13-cis to an all-trans configuration that contains a twisted chain (with high amplitude hydrogen out-of-plane vibrational bands) triggers proton transfer from Asp-85 to Glu-204 or directly to the extracellular surface, and the proton transfer in turn triggers relaxation of the twist in the retinal. The involvement of the proton transfer in the kinetics of this sequence suggests the reason for the unidirectionality of the overall reaction: upon reisomerization of the retinal the very low pK{sub a} of Asp-85 in the unphotolyzed protein is reestablished and this residue thereby becomes a good proton donor. 56 refs., 5 figs.

• DOE Contract Number: FG03-86ER13525; FG02-92ER20089
• OSTI ID: 569158
• Journal Information: Biochemistry (Eaton), Journal Name: Biochemistry (Eaton) Journal Issue: 48 Vol. 35; ISSN 0006-2960; ISSN BICHAW
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
55 BIOLOGY AND MEDICINE
BASIC STUDIES
BACTERIA
ELECTRIC POTENTIAL
FREE ENERGY
ISOMERIZATION
MEMBRANE TRANSPORT
MUTANTS
PH VALUE
PHOTOCHEMICAL REACTIONS
PORINS
PRESSURE DEPENDENCE
PROTEIN STRUCTURE
PROTEINS
PROTON TRANSPORT
REACTION KINETICS
RELAXATION
RHODOPSIN
SPECTROSCOPY
TEMPERATURE DEPENDENCE
VIBRATIONAL STATES