ELECTRON-PARAMAGNETIC-RESONANCE STUDIES OF FERRIC CYTOCHROME C' FROM PHOTOSYNTHETIC BACTERIA

Electronic ground nature of ferric cytochromes c' isolated from five p hotosynthetic bacteria, Chromatium vinosum ATCC 17899, Rhodobacter cap sulatus ATCC 11166, Rhodopseudomonas palustris ATCC 17001, Rhodospiril lum molischianum ATCC 14031, and Rhodospirillum rubrum ATCC 11170 has been investigated by electron paramagnetic resonance (EPR) spectroscop y. EPR spectra indicate that the electronic ground state of five ferri c cytochromes c' is a quantum mechanical admired-spin state of a high spin (S = 5/2) and an intermediate spin (S = 3/2) at pH 7.2 and is hig h-spin state at, pH 11.0. At physiological pH, however, the content of an intermediate spin state differs with the bacterial source of the p rotein: approximate to 50%, Chromatium vinosum; approximate to 40%, Rh odobacter capsulatus and Rhodopseudomonas palustris; approximate to 10 %, Rhodospirillum molischianum and Rhodospirillum rubrum. Computer sim ulation of the spectra supports this diversity of the contribution of an intermediate spin state. Model studies of the ferric porphyrin comp lexes suggest that the correlation between content of an intermediate spin state and heme iron displacement from the mean heme plane. Theref ore, the variation of the content of an intermediate spin state observ ed in the present study reflects the subtle difference in the degree o f heme iron displacement among the proteins.