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

Abstract

A model description of the Mo «ssbauer spectrum (80 K) of native membranes of the thermophilic cyanobacterium Synechococcus elongatus is suggested on the basis of the known values of quadrupole splitting (v vE Q ) and isomer shift (N N 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 v vE Q = 3.10 mm/s and N N 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.z 1999 Federation of European Biochemical Societies.