Cytochrome b-245 of the neutrophil superoxide-generating system contains two nonidentical hemes. Potentiometric studies of a mutant form of gp91phox.
Analysis of potentiometric titrations of the cytochrome b-245 from a X+ chronic granulomatous disease patient with an Arg54 --> Ser mutation in gp91phox indicates that the mutant form of the cytochrome contains two nonidentical hemes with midpoint potentials of Em7 = -220 and Em7 = -300 mV. In the light of this information, reanalysis of redox titrations of wild-type cytochrome b-245 implies that it probably also contains two separate heme centers with midpoint potentials of Em7 = -225 and Em7 = -265 mV. The effect of the Arg54 --> Ser substitution is to reduce the midpoint potential of one of the heme centers by approximately 35 mV and suggests possible interaction between Arg54 and a heme propionate side chain.
Cross
A R
AR
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037, USA.
Rae
J
J
Curnutte
J T
JT
D003573:Cytochrome b Group / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006801:Humans; D009154:Mutation; D009504:Neutrophils / Q000378:metabolism*; D011199:Potentiometry; D013481:Superoxides / Q000378:metabolism*
D003573:Cytochrome b Group; C035130:cytochrome b245; D013481:Superoxides; D006418:Heme