TABLE 3.

Enzymatic characteristics of the two cytochromes bd from E. coli^a

Cytochrome	Vmax (mol O/mol cytochrome bd/s)	Km (O2) at pH 7 (μM)	Km (UQ-H2) at pH 7 (μM)	Cellular content (nmol/g protein)	In vivo sp act (mol O2/mol cytochrome bd/s)
Cytochrome bd-I	218 ± 20	0.3b	85 ± 5	90 ± 29	58 ± 11
Cytochrome bd-II	818 ± 75	2.0 ± 0.3	250 ± 45	91 ± 32	70 ± 12
Cytochrome bo	225c	6.0d	47e	ND	ND

^aIn vitro V_max and K_m were determined as described in Materials and Methods. For the in vivo specific activity of the two quinol oxidases, the oxygen fluxes measured in continuous cultures (see Table 2) were divided by the measured cytochrome bd content per gram of cells (n = 3). ND, not determined.

^bData from references 25 and 31.

^cData from reference 34.

^dData from reference 25.

^eData from reference 34.