Oxygenated complex of cytochrome bd from Escherichia coli:: Stability and photolability

Cytochrome bd is one of the two terminal ubiquinol oxidases in the respiratory chain of Escherichia coli catalyzing reduction of O-2 to H2O. The enzyme is expressed under low oxygen tension; due to high affinity for O-2 it is isolated mainly as a stable oxygenated complex. Direct measurement of O-2 binding to heme d in the one-electron reduced isolated enzyme gives K-d(O2) of similar to 280 nM. It is possible to photolyse the heme d oxy-complex by illumination of the enzyme for several minutes under microaerobic conditions; the light-induced difference absorption spectrum is virtually identical to the inverted spectrum Of 02 binding to heme d. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.