CYTOCHROME-B(-245) OF THE NEUTROPHIL SUPEROXIDE-GENERATING SYSTEM CONTAINS 2 NONIDENTICAL HEMES - POTENTIOMETRIC STUDIES OF A MUTANT FORM OF GP91(PHOX)

Analysis of potentiometric titrations of the cytochrome b(-245) from a X(+) chronic granulomatous disease patient with an Arg(54) --> Ser mutation in gp91(phox) indicates that the mutant form of the cytochrome contains two nonidentical hemes with midpoint potentials of E(m7) = -220 and E(m7) = -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 E(m7) = -225 and E(m7) = -265 mV. The effect of the Arg(54) --> Ser substitution is to reduce the midpoint potential of one of the heme centers by approximately 35 mV and suggests possible interaction between Arg(54) and heme propionate side chain.