Premium
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
Author(s) -
Yang Ke,
Borisov Vitaliy B.,
Konstantinov Alexander A.,
Gennis Robert B.
Publication year - 2008
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2008.09.038
Subject(s) - ubiquinol , chemistry , catalytic cycle , cytochrome , catalysis , turnover number , electron transport chain , kinetics , enzyme , electron transfer , cytochrome c , electron donor , photochemistry , enzyme kinetics , cytochrome c oxidase , oxidase test , ferric , stereochemistry , biochemistry , coenzyme q – cytochrome c reductase , active site , inorganic chemistry , mitochondrion , physics , quantum mechanics
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.