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The reaction of cytochrome o in escherichia coli with oxygen low temperature kinetic and spectral studies

Biochemical Journal 184(2): 379-390

The reaction of cytochrome o in escherichia coli with oxygen low temperature kinetic and spectral studies

The reactions of cytochrome o in intact cells of aerobically grown E. coli with O2 and CO were studied at low temperature. Flash photolysis of CO-liganded cells in the presence of O2 and at temperatures between -79 and C results in the oxidation of kinetically heterogeneous b-type cytochromes (including cytochrome o), but not of cytochrome d. The reaction of reduced cytochrome o with O2 involves O2 binding to give intermediate(s) with spectral characteristics similar to that of the reduced oxidase-CO complex. Observation in the .alpha.-region suggests that unexplained ligand dissociation accompanies the initial O2 binding. At temperatures below C, an end point in the reaction is reached; further reaction and oxidation of cytochrome o occurs on raising the temperature. There is a linear relationship between the rate of formation of the oxygen compound and the O2 concentration up to 0.5 mM. The 2nd-order constant for its formation (k+1) is 0.91 M-1 .cntdot. s-1 at C. The reaction is not readily reversible, the value of k-1 being 1.4 .times. 10-5 s-1 and the Kd 1.5 .times. 10-5 M. The energy of activation for this reaction at low temperatures is 29.9 kJ (7.1 kcal)/mol. The reaction with O2 is distinguished from that with CO by the markedly lower velocity and high photolytic reversibility of the latter. Comparisons are drawn between the intermediate(s) in the O2 reaction of cytochrome o in E. coli and those identified in other bacteria and in the reaction of cytochrome aa3 with O2.

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Accession: 006746752

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