A comparative study of the thermal stability of plastocyanin, cytochrome c(6) and Photosystem I in thermophilic and mesophilic cyanobacteria.
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.
Balme
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A
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.
Hervás
M
M
Campos
L A
LA
Sancho
J
J
De la Rosa
M A
MA
Navarro
J A
JA