Molecular changes following oxidoreduction of cytochrome b559 characterized by Fourier transform infrared difference spectroscopy and electron paramagnetic resonance: photooxidation in photosystem II and electrochemistry of isolated cytochrome b559 and iron protoporphyrin IX-bisimidazole model compounds

• Published in: Biochemistry (Easton) 1992-11, Vol.31 (46), p.11460-11471
• Main Authors: Berthomieu, Catherine, Boussac, Alain, Maentele, Werner, Breton, Jacques, Nabedryk, Eliane
• Format: Article
• Language: English
• Subjects: Biochemistry, Molecular Biology; Biophysics; bisimidazole; bismethylimidazole; CITOCHROMO B; Cold Temperature; CYTOCHROME B; Cytochrome b Group - chemistry; cytochrome b559; E.S.R; Electrochemistry; Electron Spin Resonance Spectroscopy; FOTOSISTEMAS; Fourier Analysis; I.R. spectroscopy; Imidazoles - chemistry; iron protoporphyrin IX; Life Sciences; Metalloporphyrins - chemistry; oxidation; Oxidation-Reduction; OXIRREDUCION; OXYDOREDUCTION; Photochemistry; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosystem II Protein Complex; PHOTOSYSTEME; Plants - enzymology; PORFIRINAS; PORPHYRINE; Protoporphyrins - chemistry; PURIFICACION; PURIFICATION; Spectrophotometry, Infrared; SPINACIA OLERACEA
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00161a026

The vibrational infrared absorption changes associated with the oxidation of cytochrome b559 (Cyt b559) have been characterized. In photosystem II (PS II) enriched membranes, low-potential (LP) and high-potential (HP) Cyt b559 were investigated by light-induced FTIR difference spectroscopy. The redox transition of isolated Cyt b559 is characterized by protein electrochemistry. On the basis of a model of the assembly of Cyt b559 with the two axial Fe ligands being histidine residues of two distinct polypeptides, each forming a transmembrane alpha-helix [Cramer, W. A., Theg, S. M., and Widger, W. R. (1986) Photosynth. Res. 10, 393-403], the bisimidazole and bismethylimidazole complexes of Fe protoporphyrin IX were electrochemically oxidized and reduced to detect the IR oxidation markers of the heme and its two axial ligands. Major bands at 1674/1553, 1535, and 1240 cm-1 are tentatively assigned to v37(CaCm), v38-(CbCb) and delta(CmH) modes, respectively; other bands at 1626, 1613, 1455, 1415, and 1337 cm-1 are assigned to porphyrin skeletal and vinyl modes. Modes at 1103 and 1075/1066 cm-1 are assigned to the 4-methylimidazole and imidazole ligands, respectively. For the isolated Cyt b559, it is shown that both the heme (at 1556-1535, 1337, and 1239 cm-1), the histidine ligands at 1 104 cm-1 and the protein (between 1600 and 1700 cm-1 and at 1545 cm-1) are affected by the charge stabilization. The excellent agreement between model compounds and isolated Cyt b559 reinforces the validity of the model of a heme iron coordinated to two histidine residues for Cyt b559. A differential signal at 1656/1641 cm-1 is assigned to peptide C==O mode(s). We speculate that this signal reflects the change in strength of a hydrogen bond formed between the histidine ligand(s) and the polypeptide backbone upon oxidoreduction of the cytochrome. In PS II membranes, the signals characteristic of Cyt b559 photooxidation are found at 1660/1652 and 1625 cm-1, for both the high- and low-potenti