Photosynthesis Research

, Volume 107, Issue 3, pp 279–286

Effect of crowding on the electron transfer process from plastocyanin and cytochrome c6 to photosystem I: a comparative study from cyanobacteria to green algae

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Abstract

Plastocyanin and cytochrome c6, the alternate donor proteins to photosystem I, can be acidic, neutral or basic; the role of electrostatics in their interaction with photosystem I vary accordingly for cyanobacteria, algae and plants. The effect of different crowding agents on the kinetics of the reaction between plastocyanin or cytochrome c6 and photosystem I from three different cyanobacteria, Synechocystis PCC 6803, Nostoc PCC 7119 and Arthrospira maxima, and a green alga, Monoraphidium braunii, has been investigated by laser flash photolysis, in order to elucidate how molecular crowding affects the interaction between the two donor proteins and photosystem I. The negative effect of viscosity on the interaction of the two donors with photosystem I for the three cyanobacterial systems is very similar, as studied by increasing sucrose concentration. Bovine serum albumin seems to alter the different systems in a specific way, probably by means of electrostatic interactions with the donor proteins. Ficoll and dextran behave in a parallel manner, favouring the interaction by an average factor of 2, although this effect is somewhat less pronounced in Nostoc. With regards to the eukaryotic system, a strong negative effect of viscosity is able to overcome the favourable effect of any crowding agent, maybe due to stronger donor/photosystem I electrostatic interactions or the structural nature of the eukaryotic photosystem I-enriched membrane particles.

Keywords

Arthrospira Cytochrome c6 Crowding Laser flash photolysis Monoraphidium Nostoc Photosystem I Plastocyanin Synechocystis 

Abbreviations

BSA

Bovine serum albumin

Cyt c6

Cytochrome c6

k2

Second-order rate constant

k20

Second-order rate constant in the absence of any added viscogen

k2/k20

Relative second-order rate constant in the presence of viscogens

kobs

Observed pseudo first-order rate constant

Pc

Plastocyanin

PSI

Photosystem I

Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  1. 1.Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la CartujaUniversidad de Sevilla & CSICSevillaSpain

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