Inorganic Fe2+ formation upon Fe-S protein thermodestruction in the membranes of thermophilic cyanobacteria: Mössbauer spectroscopy study

Abstract A model description of the Mossbauer spectrum (80 K) of native membranes of the thermophilic cyanobacterium Synechococcus elongatus is suggested on the basis of the known values of quadrupole splitting (Δ E Q ) and isomer shift ( δ Fe ) for the iron-containing components of the photosynthetic apparatus. Using this approach, we found that heating the membranes at 70–80 K results in a decrease of doublet amplitudes belonging to F X , F A , F B and ferredoxin and simultaneous formation of a new doublet with Δ E Q =3.10 mm/s and δ Fe =1.28 mm/s, typical of inorganic hydrated forms of Fe 2+ . The inhibition of electron transfer via photosystem I to oxygen, catalyzed by ferredoxin, occurs within the same range of temperatures. The data demonstrate that the processes of thermoinduced Fe 2+ formation and distortions in the photosystem I electron transport in the membranes are interrelated and caused mainly by the degradation of ferredoxin. The possible role of Fe 2+ formation in the damage of the photosynthetic apparatus resulting from heating and the action of other extreme factors is discussed.