Thermal behavior of long wavelength absorption transitions in Spirulina platensis photosystem I trimers

29Citations
Citations of this article
11Readers
Mendeley users who have this article in their library.

Abstract

In photosystem I trimers of Spirulina platensis a major long wavelength transition is irreversibly bleached by illumination with high-intensity white light. The photobleaching hole, identified by both absorption and circular dichroism spectroscopies, is interpreted as the inhomogeneously broadened Q(y) transition of a chlorophyll form that absorbs maximally near 709 nm at room temperature. Analysis of the mean square deviation of the photobleaching hole between 80 and 300 K, in the linear electron-phonon frame, indicates that the optical reorganization energy is 52 cm-1 four times greater than that for the bulk, short-wavelength-absorbing chlorophylls, and the inhomogenous site distribution bandwidth is close to 150 cm-1. The room temperature bandwidth, close to 18.5 nm, is dominated by thermal (homogeneous) broadening. Photobleaching induces correlated circular dichroism changes, of opposite sign, at 709 and 670 nm, which suggests that the long wavelength transition may be a low energy excitonic band, in agreement with its high reorganization energy. Clear identification of the 709-nm spectral form was used in developing a Gaussian description of the long wavelength absorption tail by analyzing the changing band shape during photobleaching using a global decomposition procedure. Additional absorption states near 720, 733, and 743 nm were thus identified. The lowest energy state at 743 nm is present in substoichiometric levels at room temperature and its presence was confirmed by fluorescence spectroscopy. This state displays an unusual increase in intensity upon lowering the temperature, which is successfully described by assuming the presence of low-lying, thermally populated states.

Cite

CITATION STYLE

APA

Cometta, A., Zucchelli, G., Karapetyan, N. V., Engelmann, E., Garlaschi, F. M., & Jennings, R. C. (2000). Thermal behavior of long wavelength absorption transitions in Spirulina platensis photosystem I trimers. Biophysical Journal, 79(6), 3235–3243. https://doi.org/10.1016/S0006-3495(00)76556-8

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Save time finding and organizing research with Mendeley

Sign up for free