A topological scheme of the heme binding histidines and the mutated residues in gp91-phox. Mutations in the gene encoding gp91-phox were detected in the four patients; H101Y (patient T.K.), E309K (patient T.H.), L420P (patient J.O.), and W516R (patient T.M.). A cytochrome P₄₅₀-like alignment: residues 78-85 FLRGSSAC⁸⁵.27 A cytosolic loop: residues 87-94: STRVRRQL.28 Taken together with previous studies on ESR and MCD spectra,29 the spectrophotometric studies on the CGD neutrophils provided a topological scheme for the locations of the hemes in gp91-phox. For details, see text.