Participation of the g = 1.9 and g = 1.82 EPR forms of the semiquinone‐iron complex, QA −·Fe2+ of photosystem II in the generation of the Q and C thermoluminescence bands, respectively

• Published in: FEBS letters 1993-12, Vol.336 (2), p.352-356
• Main Authors: Demeter, S., Goussias, Ch, Bernát, G., Kovács, L., Petrouleas, V.
• Format: Article
• Language: English
• Subjects: Benzoquinones - chemistry; Charge recombination; Chl, chlorophyl; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea; Electron Spin Resonance Spectroscopy; EPR; EPR, electron paramagnetic resonance; Hot Temperature; Iron - chemistry; Light; Luminescence; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosystem II; Photosystem II Protein Complex; PS II, photosystem II; QA and QB, primary and secondary quinone acceptors of PS II; Semiquinone-iron complex; Thermoluminescence; TL, thermoluminescence; YD, tyrosine-160 on the D2 protein, accessory electron donor in PS II
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(93)80836-J

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about 0°C (Q band) and +50°C (C band) in the glow curve were investigated by comparative TL and EPR measurements in DCMU‐treated photosystem II particles. Decay half‐time measurements carried out at −25°C and +25°C, respectively, suggest that the S2 state (multi‐line signal) undergoes charge recombination with the g = 1.9 form of the semiquinone‐iron complex, QA −·Fe2+, resulting in the appearance of the Q band, and that the g = 1.82 form of QA −·Fe2+ back‐reacts with the oxidized tyrosine, YD + (Signal IIs), accounting for the generation of the C band.