Bioorganic chemistry of the purple membrane of Halobacterium halobium—Chromophore and apoprotein modified bacteriorhodopsins.
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Date
1988-03
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Abstract
Iodophenyl and anthryl retinal analogues have been synthesized. The transisomers
have been isolated and purified by high pressure liquid chromatography. The
purified isomers have been further characterized by nuclear magnetic resonance and
ultraviolet-visible spectroscopy. Incubation of these retinal analogues with apoprotein
(bacterioopsin), isolated from the purple membrane of Halobacterium halobium gave new
bacteriorhodopsin analogues. These analogues have been investigated for their absorption
properties and stability. The iodophenyl analogue has been found to bind to bacterioopsin
rapidly. The pigment obtained from this analogue showed a dramatically altered opsin shift
of 1343 cm-1. The anthryl analogue based bacteriorhodopsin, however, showed an opsin
shift of 3849 cm-1. It has been found that bacteriorhodopsin is quite unrestrictive in the
ionone ring site. The apoprotein seems to prefer chromophores that have the ring portion
co-planar with the polyene side chain.
The purple membrane has also been modified by treatment with fluorescamine, a surface
active reagent specific for amino groups. Reaction under controlled stoichiometric
conditions resulted in the formation of a modified pigment. The new pigment showed a
band at 390 nm–indicative of fluorescamine reaction with amino group (s) of apoprotein
–besides retaining its original absorption band at 560 nm. Analysis of the fluorescamine
modified bacteriorhodopsin resulted in the identification of lysine 129 as the modified
amino acid residue. Fluorescamine-modified-bacteriorhodopsin suspension did not release
protons under photolytic conditions. However, proteoliposomes of fluorescamine-modifiedbacteriorhodopsin
were found to show proton uptake, though at a reduced rate.
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Keywords
Bacteriorhodopsin, purple membrane, bacteriorhodopsin chemical modifications, proton pumping, bacteriorhodopsin analogues
Citation
Singh Anil K, Roy M, Sonar S, Kapil M. Bioorganic chemistry of the purple membrane of Halobacterium halobium—Chromophore and apoprotein modified bacteriorhodopsins. Journal of Biosciences. 1988 Mar; 13(1): 55-59.