Graan T, Ort DR. Quantitation of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone binding sites in chloroplast membranes: evidence for a functional dimer of the cytochrome b6f complex.
Arch Biochem Biophys 1986;
248:445-51. [PMID:
3740838 DOI:
10.1016/0003-9861(86)90497-2]
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Abstract
The binding of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) to chloroplast thylakoid membranes was investigated by analyzing the inhibition of electron transfer by DBMIB according to a steady-state rate relationship for enzyme-catalyzed reactions in the presence of tightly binding reversible inhibitors. DBMIB interacts with the cytochrome b6f complex in a manner best described by an apparent dissociation constant near 6 nM. The binding site titer is 1 mmol X mol chlorophyll-1. This number of DBMIB binding sites approaches one-half the number of cytochrome b6f complexes present in the membrane. These data suggest that the cytochrome b6f complex may function in electron transfer as a dimer, plastoquinol oxidation being totally inhibited by the binding of a single DBMIB molecule to the dimer.
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