CHARACTERIZATION OF A REDOX-ACTIVE CROSS-LINKED COMPLEX BETWEEN CYANOBACTERIAL PHOTOSYSTEM-I AND ITS PHYSIOLOGICAL ACCEPTOR FLAVODOXIN

Citation
U. Muhlenhoff et al., CHARACTERIZATION OF A REDOX-ACTIVE CROSS-LINKED COMPLEX BETWEEN CYANOBACTERIAL PHOTOSYSTEM-I AND ITS PHYSIOLOGICAL ACCEPTOR FLAVODOXIN, EMBO journal, 15(3), 1996, pp. 488-497
Citations number
47
Categorie Soggetti
Biology,"Cell Biology
Journal title
ISSN journal
02614189
Volume
15
Issue
3
Year of publication
1996
Pages
488 - 497
Database
ISI
SICI code
0261-4189(1996)15:3<488:COARCC>2.0.ZU;2-C
Abstract
A covalent complex between photosystem I and flavodoxin from the cyano bacterium Synechococcus sp, PCC 7002 was generated by chemical cross-l inking, Laser flash-absorption spectroscopy indicates that the bound f lavodoxin of this complex is stabilized in the semiquinone state and i s photoreduced to the quinol form upon light excitation. The kinetics of this photoreduction process, which takes place in similar to 50% of the reaction centres, displays three exponential components with half -lives of 9 mu s, 70 mu s and 1 ms. The fully reduced flavodoxin subse quently recombines with P700(+) with a t(1/2) of 330 ms. A correspondi ng flavodoxin semiquinone radical signal is readily observed in the da rk by room temperature electron paramagnetic resonance, which reversib ly disappears upon illumination. In contrast, the light-induced reduct ion of oxidized flavodoxin can be observed only by first-flash experim ents following excessive dark adaptation. In addition, the docking sit e of flavodoxin on photosystem I was determined by electron microscopy in combination with image analysis, Flavodoxin binds to the cytoplasm ic side of photosystem I at a distance of 7 nm from the centre of the trimer and in close contact to a ridge formed by the subunits PsaC, Ps aD and PsaE.