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Science 25 January 1985:
Vol. 227. no. 4685, pp. 419 - 423
DOI: 10.1126/science.227.4685.419
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Articles

Disk-to-Disk Transfer as the Rate-Limiting Step for Energy Flow in Phycobilisomes

A. N. GLAZER 1, SHEILA W. YEH 2, S. P. WEBB 2, and J. H. CLARK 2

1 Department of Microbiology and Immunology, University of California, Berkeley 94720
2 Laboratory of Chemical Dynamics, Lawrence Berkeley Laboratory, and Department of Chemistry, University of California, Berkeley 94720

A broadly tunable picosecond laser source and an ultrafast streak camera were used to measure temporally and spectrally resolved emission from intact phycobilisomes and from individual phycobiliproteins as a function of excitation wavelength. Both wild-type and mutant phycobilisomes of the unicellular cyanobacterium Synechocystis 6701 were examined, as well as two biliproteins, R-phycoerythrin (240 kilodaltons, 34 bilins) and allophycocyanin (100 kilodaltons, 6 bilins). Measurements of intact phycobilisomes with known structural differences showed that the addition of an average of 1.6 phycoerythrin disks in the phycobilisome rod increased the overall energy transfer time by 30 ± 5 picoseconds. In the isolated phycobiliproteins the onset of emission was as prompt as that of a solution of rhodamine B laser dye and was independent of excitation wavelength. This imposes an upper limit of 8 picoseconds (instrument-limited) on the transfer time from "sensitizing" to "fluorescing" chromophores in these biliproteins. These results indicate that disk-to-disk transfer is the slowest energy transfer process in phycobilisomes and, in combination with previous structural analyses, show that with respect to energy transfer the lattice of approximately 625 light-harvesting chromophores in the Synechocystis 6701 wild-type phycobilisome functions as a linear five-point array.

Submitted on August 2, 1984
Accepted on September 24, 1984


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Role of phycoerythrin in marine picoplankton Synechococcus spp.
S. Yeh, L. Ong, and A. Glazer (1986)
Science 234, 1422-1424
   PDF »
Kinetics of Energy Flow in the Phycobilisome Core.
A. N. GLAZER, C. CHAN, R. C. WILLIAMS, S. W. YEH, and J. H. CLARK (1985)
Science 230, 1051-1053
   Abstract »    PDF »


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