The fully oxidized form of the cytochrome bd quinol oxidase from E. coli does not participate in the catalytic cycle: direct evidence from rapid kinetics studies.
Cytochrome bd catalyzes the two-electron oxidation of either ubiquinol or menaquinol and the four-electron reduction of O(2) to H(2)O. In the current work, the rates of reduction of the fully oxidized and oxoferryl forms of the enzyme by the 2-electron donor ubiquinol-1 and single electron donor N,N,N',N'-tetramethyl-p-phenylendiamine (TMPD) have been examined by stopped-flow techniques. Reduction of the all-ferric form of the enzyme is 1000-fold slower than required for a step in the catalytic cycle, whereas the observed rates of reduction of the oxoferryl and singly-reduced forms of the cytochrome are consistent with the catalytic turnover. The data support models of the catalytic cycle which do not include the fully oxidized form of the enzyme as an intermediate.
Yang
Ke
K
Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA.
Borisov
Vitaliy B
VB
Konstantinov
Alexander A
AA
Gennis
Robert B
RB
D002384:Catalysis; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D045222:Electron Transport Chain Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D007700:Kinetics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D013772:Tetramethylphenylenediamine / Q000737:chemistry; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000737:chemistry
D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D014451:Ubiquinone; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli; C003741:ubiquinol; D013772:Tetramethylphenylenediamine