tailieunhanh - Báo cáo khoa học: Cytochrome b6f is a dimeric protochlorophyll a binding complex in etioplasts

The cytochrome b6f complex is a dimeric protein complex that is of central importance for photosynthesis to carry out light driven electron and proton transfer in chloroplasts. One molecule of chlorophyll awas found to asso-ciate per cytochrome b6 f monomer and the structural or functional impor-tance of this is discussed. | ễFEBS Journal Cytochrome b6f is a dimeric protochlorophyll a binding complex in etioplasts Veronika Reisinger Alexander P. Hertle Matthias Ploscher and Lutz A. Eichacker Department Biology I University Munich Germany Keywords chlorophyll cytochrome b6f etioplast protochlorophyll Correspondence L. A. Eichacker Department Biology I University Munich Menzingerstrasse 67 80638 Munich Germany Fax 49 89 17861 209 Tel 49 89 17861 272 E-mail Received 30 October 2007 revised 20 December 2007 accepted 2 January 2008 doi The cytochrome b6f complex is a dimeric protein complex that is of central importance for photosynthesis to carry out light driven electron and proton transfer in chloroplasts. One molecule of chlorophyll a was found to associate per cytochrome b6f monomer and the structural or functional importance of this is discussed. We show that etioplasts which are devoid of chlorophyll a already contain dimeric cytochrome b6f. However the phyty-lated chlorophyll precursor protochlorophyll a and not chlorophyll a is associated with subunit b6. The data imply that a phytylated tetrapyrrol is an essential structural requirement for assembly of cytochrome b6f. In respiration and photosynthesis cytochrome binding protein complexes Cyt of the bc1 Cyt bc1 and b6f type Cyt b6f couple hydrogen and electron transfer across a membrane phase 1 . In the Cyt b6f complex two protons per electron are translocated across the membrane to build up an electrochemical gradient for the generation of ATP 2 . Seven prosthetic groups per monomer Cyt b6f complex have been identified. One 2 Fe-2 S-cluster four hemes one c- two b- and one x-type one chlorophyll a Chl and one b-carotene were described per monomer 3 . The participation of hemes in the electron transport process is indisputable. Chl was found in Cyt b6f preparations of both pro- and eukaryotic origin 3-6 and b-carotene was shown to be echine-none in the prokaryote .