Heme-heme interactions in the cytochrome b6f complex: EPR spectroscopy and correlation with structure.
Cytochrome b6f of oxygenic photosynthesis was studied using multifrequency, multimode EPR Spectroscopy. Frequency dependent signals above g = 4.3, and the observation of parallel-mode signals, are indicative of spin interactions in the complex. We demonstrate the presence of an exchange interaction between the unique high-spin heme cn and a nearby low-spin heme bn, and show that a quinone analog NQNO binds at or near to heme cn. The two hemes remain spin coupled upon the binding of NQNO, though strength of interaction decreases significantly. The electronic coupling implies that the heme bn/cn pair could function as a unit to facilitate 2-electron reduction of plastoquionone without generation of an energetically unfavorable semiquinone intermediate.
Zatsman
Anna I
AI
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Zhang
Huamin
H
Gunderson
William A
WA
Cramer
William A
WA
Hendrich
Michael P
MP
D003545:Cysteine / Q000737:chemistry; D045346:Cytochrome b6f Complex / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D015394:Molecular Structure
D006418:Heme; D006639:Histidine; D045346:Cytochrome b6f Complex; D003545:Cysteine