title: A comparative study of the thermal stability of plastocyanin, cytochrome c(6) and Photosystem I in thermophilic and mesophilic cyanobacteria.
abstract: Cytochrome c(6) (Cyt) from the thermophilic cyanobacterium Phormidium laminosum has been purified and characterized. It is a mildly acidic protein, with physicochemical properties very similar to those of plastocyanin (Pc). This is in agreement with the functional interchangeability of the two metalloproteins as electron donors to Photosystem I (PS I). The kinetic analyses of the interaction of Pc and Cyt with Photosystem I show that both metalloproteins reduce PS I with similar efficiencies, according to an oriented collisional kinetic model involving repulsive electrostatic interactions. The thermostability study of the Phormidium Pc/PS I system compared with those from mesophilic cyanobacteria (Synechocystis, Anabaena and Pseudanabaena) reveals that Pc is the partner limiting the thermostability of the Phormidium couple. The cross-reactions between Pc and PS I from different organisms demonstrate not only that Phormidium Pc enhances the stability of the Pc/PS I system using PS I from mesophilic cyanobacteria, but also that Phormidium PS I possesses a higher thermostability than the other photosystems.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Universidad de Sevilla y CSIC, 41092, Sevilla, Spain, marosa@cica.es.
authors.forename: A
authors.initials: A
authors.lastname: Balme
authors.forename: M
authors.initials: M
authors.lastname: Hervás
authors.forename: L A
authors.initials: LA
authors.lastname: Campos
authors.forename: J
authors.initials: J
authors.lastname: Sancho
authors.forename: M A
authors.initials: MA
authors.lastname: De la Rosa
authors.forename: J A
authors.initials: JA
authors.lastname: Navarro