Proton-linked second electron transfer

Several amino acid residues of H form electrostatically coupled clusters ofionizable residues near Qb (Lancaster et al., 1996). In the Rb. sphaeroides RC, Glu H173 is a member of a cluster which also includes Asp L213, a residue required for proton uptake by Qb (see below). Mutation of Glu HI 73 to Gin retards both the kinetics of the first electron transfer and of the proton-linked second electron transfer (Takahashi and Wraight, 1996). Another characteristic for the region proximal to and Qb are clusters of firmly bound water molecules (Abresch etal., 1998 Fritzsch etal., 1998). Several side chains... 

In a redox system consisting of a peroxo compound and an iron(II) salt, the initiating radicals are formed by electron transfer from Fe " to the peroxo compound, causing the peroxy link to be cleaved, with simultaneous formation of a radical and an anion. In a second step, the oxidized metal reacts with another hydroperoxide to form a peroxy radical and a proton ... 

A principal product formed by irradiating quinoline-2-carbonitrile (35) in acidified aqueous propan-2-ol has two quinoline rings linked through the 2-4 positions and has lost both cyano-groups. The mechanism put forward for this formal 1,2-addition reaction begins with electron transfer from propan-2-ol to an upper triplet state of protonated (35), followed by attack on a second (ground-state) molecule of (35). A photophysical study of the photoreduction of acridine... 

A second heme (heme a) and a second copper (Cua) mediate the transfer of electrons from cytochrome c to the dinuclear center. The electron transfer process is directly linked to proton translocation across the cell membrane and the 02-reduction reaction. The electrochemical potential gradient generated by this proton-pumping process is ultimately used in the synthesis of ATP. 

What is the nature of the proton-translocating pumps that link Ap with electron transport In his earliest proposals Mitchell suggested that electron carriers, such as flavins and ubiquinones, each of which accepts two protons as well as two electrons upon reduction, could serve as the proton carriers. Each pump would consist of a pair of oxidoreductases. One, on the inside (matrix side) of the coupling membrane, would deliver two electrons (but no protons) to the carrier (B in Fig. 18-13). The two protons needed for the reduction would be taken from the solvent in the matrix. The second oxidoreductase would be located on the outside of the membrane and would accept two electrons from the reduced carrier (BH2 in Fig. 18-13) leaving the two released protons on the outside of the membrane. To complete a "loop" that would allow the next carrier to be reduced, electrons would have to be transferred through fixed electron carriers embedded in the... 

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