Affordable Access

Primary intermediates in the photochemical cycle of bacteriorhodopsin.

Authors
  • Applebury, M L
  • Peters, K S
  • Rentzepis, P M
Type
Published Article
Journal
Biophysical journal
Publication Date
Sep 01, 1978
Volume
23
Issue
3
Pages
375–382
Identifiers
PMID: 698342
Source
Medline
License
Unknown

Abstract

Picosecond studies of the primary photochemical events in the light-adapted bacteriorhodopsin, bR570, indicate that the first metastable intermediate K610 is formed with a rise time of 11 ps. Difference spectra obtained at 50 ps after excitation show that K610 is the same species as that trapped in low temperature glasses. A precursor species (S) of the K610 intermediate has been observed which is red shifted with respect to K610 and is formed within the 6-ps time width of the excitation pulse. The formation of the precursor has no observable thermal dependence between 298 degrees and 1.8 degrees K. The formation of K610 has a very low thermal barrier and at very low temperatures, the rate of formation becomes practically temperature independent which is characteristic of a tunneling process. The rate of formation becomes practically temperature independent which is characteristic of a tunneling process. The rate of formation of K610 has a moderate deuterium isotope effect of kH/kD approximately 1.6 at 298 degrees K and 2.4 at 4 degrees K. The mechanism for formation of K610 is found to involve a rate-limiting proton transfer which occurs by tunneling at low temperatures.

Report this publication

Statistics

Seen <100 times