ISSN:
0377-0486
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Experiments with a spinning cell and a single continuous-wave laser beam (514 nm) in reflection geometry were performed to obtain the resonance Raman (RR) spectra of the intermediate K590 of the retinal chromophore of bacteriorhodopsin (bR). Samples of diluted aqueous suspensions of ‘purple membranes’ from Halobacterium halobium were used, which entail bR as an integral protein. K590 is formed photochemically in ca. 5 ps from the parent chromophore BR570 and in H2O decays into the product L550 with a time constant of ca. 1.2 μs (21°C). Using a flow velocity of ca. 20 m s-1 and a beam waist of 40 μm, the integrated relative concentrations of BR570, K590 and L550 in the beam were 58:33:10, respectively. By this method the ‘late’ K intermediate which is accumulated on a time scale of ca. 1 μs was probed. The spectra of the mixture were recorded with a spectral step width of 0.2 cm-1 and a band width of 4 cm-1. Up to 100 scans were accumulated to obtain the high quality which is required for subtraction and band-fitting procedures. The contributions of BR570 and L550, whose spectra were obtained in separate experiments, were subtracted leaving the pure spectra of K590. Experiments were performed in H2O and D2O suspensions. Structural changes of the chromophore during the transition from K590 to L550 were inferred from the RP spectra in the hydrogen out-of-plane, the fingerprint and the C=C/C=N stretching regions. It was concluded that in this transition the chromophore relaxes from a distorted to a planar conformation and at the same time a positive charge of the protein envelope approaches the β-ionone ring of retinal. It is proposed that this electrostatic interaction is important for the biological function of bR.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jrs.1250231010
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