title: Detection of the photosystem I:ferredoxin complex by backscattering interferometry.
abstract: The dissociation constant K(d) of the photosystem I (PSI):ferredoxin complex has been measured by backscattering interferometry (BSI) with cyanobacterial PSI (350 kDa) and ferredoxin (10.5 kDa). The BSI signal, consisting of shifts for interference fringes resulting from a change in refractive index due to complex formation, was monitored as ferredoxin concentration was titrated. K(d) values of 0.14-0.38 microM were obtained with wild-type PSI whereas no complex was detectable with a PSI mutant containing a single mutation (R39Q) in the PsaE extrinsic subunit. These results are in quantitative agreement with previous functional determinations consisting in the detection of fast electron transfer within the complex. They provide evidence that the main contribution for the high affinity binding of ferredoxin to PSI is due to a single region of PsaE comprising arginine 39. They do not support the existence of a secondary binding site that could have escaped functional detection.
authors.affiliation: iBiTec-S, URA CNRS 2096, CEA Saclay, 91191 Gif sur Yvette, France. pierre.setif@cea.fr
authors.forename: Pierre
authors.initials: P
authors.lastname: Sétif
authors.forename: Nathan
authors.initials: N
authors.lastname: Harris
authors.forename: Bernard
authors.initials: B
authors.lastname: Lagoutte
authors.forename: Stephen
authors.initials: S
authors.lastname: Dotson
authors.forename: Scot R
authors.initials: SR
authors.lastname: Weinberger
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics; D005288:Ferredoxins / Q000737:chemistry*; D008958:Models, Molecular; D009154:Mutation; D045331:Photosystem I Protein Complex / Q000737:chemistry*
chemical_list: D005288:Ferredoxins; D045331:Photosystem I Protein Complex