Picosecond time-resolved resonance Raman spectroscopy of bacteriorhodopsin's J, K, and KL intermediates

Resonance Raman spectroscopy has been used to obtain structural and kinetic information on the primary photointermediates of bacteriorhodopsin with 3-ps time resolution. A synchronously pumped dye laser was amplified at 50 Hz to produce a probe pulse at 589 nm while a second, spectrally distinct, pu...

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Veröffentlicht in:Journal of physical chemistry (1952) 1991-08, Vol.95 (16), p.6372-6379
Hauptverfasser: Doig, Stephen J, Reid, Philip J, Mathies, Richard A
Format: Artikel
Sprache:eng
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Zusammenfassung:Resonance Raman spectroscopy has been used to obtain structural and kinetic information on the primary photointermediates of bacteriorhodopsin with 3-ps time resolution. A synchronously pumped dye laser was amplified at 50 Hz to produce a probe pulse at 589 nm while a second, spectrally distinct, pump pulse at 550 nm was generated by amplification of a 10-nm portion of a continuum produced from the probe pulse. This apparatus was used to record Stokes Raman spectra of the photoproduct from 0 ps to 13 ns as well as anti-Stokes spectra from 0 to 10 ps. At 0 ps, the Stokes spectrum, assigned to J, has strong hydrogen out-of-plane (HOOP) intensity at 1,000 and 956 cm{sup {minus}1}, the fingerprint region consists of a broad band of lines from 1,155 to 1,200 cm{sup {minus}1}, and the ethylenic line is found at 1,518 cm{sup {minus}1}. By 3 ps the relative HOOP intensity drops to its lowest value and the fingerprint collapses to a single strong mode at 1,189 cm{sup {minus}1}, while the ethylenic remains at 1,518 cm{sup {minus}1}. The lifetime of the initially strong anti-Stokes scattering is {approximately}2.5 ps, indicating that the J {yields} K transition is due, in large part, to vibrational cooling of the chromophore. The authors conclude that the chromophore in J is highly twisted and thermally excited but that it cools and conformationally relaxes to a more planar 13-cis chromophore within 3 ps to form K. Between 3 and 40 ps there is a resurgence in Stokes HOOP intensity which remains large and nearly constant thereafter and the ethylenic frequency shifts from 1,518 to 1,521 cm{sup {minus}1} within 200 ps. These changes are assigned to the conversion of K to a more twisted and bluer-absorbing KL species between 20 and 100 ps which must be caused by an isomerization-induced protein conformational change.
ISSN:0022-3654
1541-5740
DOI:10.1021/j100169a054