Replacement of leucine-93 by alanine or threonine slows down the decay of the N and O intermediates in the photocycle of bacteriorhodopsin: Implications for proton uptake and 13-cis-retinal----all-trans-retinal reisomerization

Journal Article · Thu Aug 01 00:00:00 EDT 1991 · Proceedings of the National Academy of Sciences of the United States of America; (United States)

DOI:https://doi.org/10.1073/pnas.88.15.6873· OSTI ID:5163382

Subramaniam, S; Greenhalgh, D A; Rath, P; Rothschild, K J; Khorana, H G ^[1]

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1. Massachusetts Institute of Technology, Cambridge (USA)

The authors report that the replacement of Leu-93 in bacteriorhodopsin by Ala (L93A) or Thr (L93T) slows down the photocycle by approximately 100-fold relative to wild-type bacteriorhodopsin. Time-resolved visible absorption spectroscopy and resonance Raman experiments, respectively, show the presence of long-lived O-like and N-like intermediates in the photocycles of the above mutants. We infer the existence of an equilibrium between the N and O intermediates in the photocycles of these mutants. The L93A and L93T mutants exhibit normal proton pumping under continuous illumination, suggesting that the decay of the N and/or O intermediate, and consequently, proton translocation, can be accelerated by the absorption of a second photon. Since the 13-cis----all-trans reisomerization of retinal is completed during the decay of the N and O intermediates, they conclude that the interaction of Leu-93 with retinal is important in this phase of the photocycle. This conclusion is supported by a recent structural model of bacteriorhodopsin that suggests that Leu-93 is near the C-13 methyl group of retinal.

• OSTI ID: 5163382
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (United States), Journal Name: Proceedings of the National Academy of Sciences of the United States of America; (United States) Vol. 88:15; ISSN 0027-8424; ISSN PNASA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTRA
AMINO ACID SEQUENCE
AMINO ACIDS
BACTERIA
BARYONS
CARBOXYLIC ACID ESTERS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CLONING
ELEMENTARY PARTICLES
ESCHERICHIA COLI
ESTERS
FERMIONS
HADRONS
HYDROXY ACIDS
ISOMERIZATION
LEUCINE
MICROORGANISMS
MOLECULAR STRUCTURE
MUTANTS
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
PIGMENTS
PROTEINS
PROTONS
RAMAN SPECTRA
RETINOIC ACID
RHODOPSIN
SPECTRA
SPECTROPHOTOMETRY
THREONINE