THE STATE OF IRON IN THE OXYGEN-EVOLVING CORE COMPLEX OF THE CYANOBACTERIUM PHORMIDIUM-LAMINOSUM - MOSSBAUER-SPECTROSCOPY

The state of iron in a purified oxygen-evolving core complex from Phor midium laminosum was characterized using Mossbauer spectroscopy at 77 K. Mossbauer spectra of the sample, as prepared, were fitted by two qu adrupole pairs corresponding to Fe of high spin (2+) and low spin (2+) . The signal of the high-spin (2+) species disappeared in the presence of the oxidant K3Fe(CN)(6). After dialysis of the oxidized sample and addition of the reductant Na2S2O4, the spectra recovered the original shape, and the signals corresponding to the high-spin (2+) and low-sp in (2+) species reappeared. Furthermore, light excitation of the sampl e at 200 K, previously oxidized with K3Fe(CN)(6) at 4 degrees C, induc ed the accumulation of the high-spin (2+) species. Based on Mossbauer and optical spectroscopy, we ascribe the high-spin and low-spin specie s to the Fe of the iron-quinone complex and to both cytochrome b-559 a nd c-549, respectively. The Mossbauer results also indicate that in th is cyanobacterium the Fe of the iron-quinone complex can undergo redox changes induced either chemically or by light. Moreover, we observe a pproximately one cytochrome b-559 per reaction center in this preparat ion.