Yuejun Zhen

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To determine the interaction site for cytochrome c (Cc) on cytochrome c oxidase (CcO), a number of conserved carboxyl residues in subunit II of Rhodobacter sphaeroides CcO were mutated to neutral forms. A highly conserved tryptophan, Trp(143), was also mutated to phenylalanine and alanine. Spectroscopic and metal analyses of the surface carboxyl mutants(More)
The epidermal growth factor receptor is a transmembrane glycoprotein that mediates the cellular responses to epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). In this study of the human EGF receptor naturally expressed in A431 cells, the glycosylation sites of the full-length, membrane-bound receptor and of a secreted form of(More)
Substoichiometric amounts of Mn are bound by the aa3-type cytochrome c oxidase of Rhodobacter sphaeroides and appear in the EPR spectrum of the purified enzyme as signals that overlay those of CuA in the g = 2.0 region. The Mn is tightly bound and not removed by a high degree of purification or by washing with 50 mM EDTA. The amount of bound Mn varies with(More)
The aa3-type cytochrome c oxidase of Rhodobacter sphaeroides has been overexpressed up to seven fold over that in wild-type strains by engineering a multicopy plasmid with all the required oxidase genes and by establishing optimum growth conditions. The two operons containing the three structural genes and two assembly genes for cytochrome c oxidase were(More)
In cytochrome c oxidase, a requirement for proton pumping is a tight coupling between electron and proton transfer, which could be accomplished if internal electron-transfer rates were controlled by uptake of protons. During reaction of the fully reduced enzyme with oxygen, concomitant with the "peroxy" to "oxoferryl" transition, internal transfer of the(More)
The reaction between cytochrome c (Cc) and Rhodobacter sphaeroides cytochrome c oxidase (CcO) was studied using a cytochrome c derivative labeled with ruthenium trisbipyridine at lysine 55 (Ru-55-Cc). Flash photolysis of a 1:1 complex between Ru-55-Cc and CcO at low ionic strength results in electron transfer from photoreduced heme c to Cu(A) with an(More)
When dioxygen is reduced to water by cytochrome c oxidase a sequence of oxygen intermediates are formed at the reaction site. One of these intermediates is called the "peroxy" (P) intermediate. It can be formed by reacting the two-electron reduced (mixed-valence) cytochrome c oxidase with dioxygen (called P(m)), but it is also formed transiently during the(More)
To study the functional significance of the unusual bimetallic Cu(A) center of cytochrome c oxidase, the direct ligands of the Cu(A) center in subunit II of the holoenzyme were mutated. Two of the mutant forms, M263L and H260N, exhibit major changes in activity (10% and 1% of wild-type, respectively) and in near-infrared and EPR spectra, but metal analysis(More)
The function of the binuclear Cu(A) center in cytochrome c oxidase (CcO) was studied using two Rhodobacter sphaeroides CcO mutants involving direct ligands of the Cu(A) center, H260N and M263L. The rapid electron-transfer kinetics of the mutants were studied by flash photolysis of a cytochrome c derivative labeled with ruthenium trisbipyridine at lysine-55.(More)
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