EPR study of cytochrome in the D1D2 Cyt b-559 complex

Study of heme Fe(III) ligated by OH– in cytochrome b–559 and its low temperature photochemistry in intact chloroplasts

“…Furthermore, the light-induced changes of the high spin EPR signal at low temperature indicate that this heme Fe(III) has to be close to P680. Accordingly, this heme is evidently Cyt b-559 in the high spin form (see [9]) and certainly not Cyt f The decrease of the g = 6.8 signal is also observed upon illumination at 80K but in this case it is accompanied by the appearance of the g = 5.8 signal much smaller in amplitude (Fig. 3b).…”

“…lc several DDQ induced signals appear between g = 2.15(1) and g = 1.85(1). Our studies [9] and comparison with model systems like myoglobin or catalase as well as with different ligated cytochromes [15] clearly show that these signals cannot be assigned to a low spin Fe(III) cytochrome. The origin of the strong rhombic iron signal at g = 4.26 (2) is not clarified [16].…”

“…A comparison of the EPR signals of the high spin heme Fe(III) in intact chloroplasts with that in Mb (at different pH) (Fig. 1) where the 6th coordination position is not occupied by a strong ligand [12], leads to the conclusion that the signal with g = 6.8 is due to the ligation of heme Fe(III) by OH at the 6th coordination position (see also [9]). This ligation probably changes the symmetry of a molecular field (e.g.…”

“…Optical and EPR studies revealed several forms of Cyt b-559 in D ID2Cyt b-559 complexes with different redox potentials at pH 7.2 and at pH 9.4 [7,9]. The optical and EPR (g = 5.9 and 6.4) properties of one form at pH 9.4 clearly show that its heme is ligated by OH at the 6th coordination position [7,9].…”

“…The optical and EPR (g = 5.9 and 6.4) properties of one form at pH 9.4 clearly show that its heme is ligated by OH at the 6th coordination position [7,9]. Although the 5th ligand of this form was suggested to be histidine [9].…”