Spectral and thermodynamic properties of the two hemes of the D1D2cytochrome b‐559 complex of spinach

FEBS Letters

Heber, U.¹  Schreiber, U.¹  Shuvalov, V.A.² 

[1] Julius-von-Sachs Institute of Biosciences, University of Würzburg, D-97082 Würzburg, Germany;Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow reg. 142292, Russian Federation

关键词: Cytochrome b-559;    D1D2 Cyt b-559 complex;    PS-II;    Cyt;    cytochrome;    E m midpoint redox potential;    HP;    IP;    LP and XLP;    high;    intermediate;    low and extra low potential forms of hemes;    respectively;    P680;    primary electron donor;    Phe;    pheophytin;    RCs;    reaction centers;    PS-II;    photosystem-II;   

DOI  :  10.1016/0014-5793(94)80196-7

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

In agreement with previous work [Shuvalov, Heber and Schreiber (1988) FEBS Lett. 258, 27-31] two hemes (low potential (LP) and extra low potential (XLP )) per two pheophytins were found in isolated D1D2Cyt b-559 complexes. Reductive and oxidative redox titrations demonstrate that the E _m of the LP form is at about +150 mV. It is independent of pH between pH 7.2 and 9.4. The XLP heme is autoxidizable at pH 7.2 and displays, at this pH, an E _m of − 45 mV. Both the LP and XLP hemes show absorption peaks at 559 nm. They are proposed to have bis-histidine ligation of the heme iron. At pH 9.4, the XLP heme splits into two forms. One of them has an E _m of +40 mV, and absorption peaks at 559 nm showing the bis-histidine ligation. The other displays an E _m of −220 mV and the peak is shifted to 562 nm. This last form is proposed to be due to the incorporation of OH⁻ which occupies the 6th coordination position of the heme Fe(III) at high pH. The pK value for the conversion of the XLP heme is close to 7.7. In a structure simulation of the α-helices of α- and β-polypeptides, the β-polypeptide, but not the α-polypeptide, reveals a distance between the histidine N and the heme Fe which permits stable N-Fe coordination. In the α-polypeptide, OH⁻ can be incorporated between N and Fe. The functional role of the two hemes of cyt b-559 is briefly discussed with respect to water oxidation and cyclic electron transfer.

【 授权许可】

Unknown