A comparative study of the thermal stability of plastocyanin, cytochrome c6 and Photosystem I in thermophilic and mesophilic cyanobacteria

• Published in: Photosynthesis research Vol. 70; no. 3; p. 281
• Main Authors: Balme, Alexis, Hervás, Manuel, Campos, Luis A, Sancho, Javier, De la Rosa, Miguel A, Navarro, José A
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.12.2001
• Subjects: Bacteria
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1023/A:1014761524242

Cytochrome c^sub 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.[PUBLICATION ABSTRACT]