In vivo photosystem I reduction in thermophilic and mesophilic cyanobacteria: the thermal resistance of the process is limited by factors other than the unfolding of the partners.
Photosystem I reduction by plastocyanin and cytochrome c(6) in cyanobacteria has been extensively studied in vitro, but much less information is provided on this process inside the cell. Here, we report an analysis of the electron transfer from both plastocyanin and cytochrome c(6) to photosystem I in intact cells of several cyanobacterial species, including a comparative study of the temperature effect in mesophilic and thermophilic organisms. Our data show that cytochrome c(6) reduces photosystem I by following a reaction mechanism involving complex formation, whereas the copper-protein follows a simpler collisional mechanism. These results contrast with previous kinetic studies in vitro. The effect of temperature on photosystem I reduction leads us to conclude that the thermal resistance of this process is determined by factors other than the proper stability of the protein partners.
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla y CSIC, Centro Isla de la Cartuja, Américo Vespucio 49, E-41092 Seville, Spain.
Raúl V
RV
Durán
Manuel
M
Hervás
Miguel A
MA
De la Rosa
José A
JA
Navarro
D000222:Adaptation, Physiological / Q000502:physiology; D000458:Cyanobacteria / Q000145:classification* / Q000378:metabolism* / Q000528:radiation effects; D045365:Cytochromes c6 / Q000378:metabolism*; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D010970:Plastocyanin / Q000378:metabolism*; D011489:Protein Denaturation / Q000528:radiation effects; D017510:Protein Folding; D013045:Species Specificity; D013696:Temperature
D045365:Cytochromes c6; D045331:Photosystem I Protein Complex; D010970:Plastocyanin