NDLI: Modification of quinone electrochemistry by the proteins in the biological electron transfer chains: examples from photosynthetic reaction centers

Content Provider	Springer Nature Link
Author	Gunner, M. R. Madeo, Jennifer Zhu, Zhenyu
Copyright Year	2008
Abstract	Quinones such as ubiquinone are the lipid soluble electron and proton carriers in the membranes of mitochondria, chloroplasts and oxygenic bacteria. Quinones undergo controlled redox reactions bound to specific sites in integral membrane proteins such as the cytochrome bc$_{1}$ oxidoreductase. The quinone reactions in bacterial photosynthesis are amongst the best characterized, presenting a model to understand how proteins modulate cofactor chemistry. The free energy of ubiquinone redox reactions in aqueous solution and in the Q$_{A}$ and Q$_{B}$ sites of the bacterial photosynthetic reaction centers (RCs) are compared. In the primary Q$_{A}$ site ubiquinone is reduced only to the anionic semiquinone (Q$^{•−}$) while in the secondary Q$_{B}$ site the product is the doubly reduced, doubly protonated quinol (QH$_{2}$). The ways in which the protein modifies the relative energy of each reduced and protonated intermediate are described. For example, the protein stabilizes Q$^{•−}$ while destabilizing Q$^{=}$ relative to aqueous solution through electrostatic interactions. In addition, kinetic and thermodynamic mechanisms for stabilizing the intermediate semiquinones are compared. Evidence for the protein sequestering anionic compounds by slowing both on and off rates as well as by binding the anion more tightly is reviewed.
Starting Page	509
Ending Page	519
Page Count	11
File Format	PDF
ISSN	0145479X
Journal	Journal of Bioenergetics and Biomembranes
Volume Number	40
Issue Number	5
e-ISSN	15736881
Language	English
Publisher	Springer US
Publisher Date	2008-11-01
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Quinone Photosynthesis E$_{m}$ Continuum electrostatics Ligand Ubiquinone Electrochemistry Bioorganic Chemistry Biochemistry Animal Anatomy / Morphology / Histology Animal Biochemistry Organic Chemistry
Content Type	Text
Resource Type	Article
Subject	Cell Biology Physiology

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