Sucrose gradient centrifugation of detergent extracts of cytoplasmic membranes. Cytoplasmic membranes of strains BW25113 (●) and BW25113 cyaY::nptI (■) were isolated. Proteins were extracted from cytoplasmic membranes with 3% dodecyl maltoside (w/v) and separated by means of gradients of 5–30% sucrose in 50 mM MES/NaOH, 50 mM NaCl, 5 mM MgCl2 and 0.1% dodecyl maltoside, pH 6.0. The gradient with the extract from the parental strain was loaded with 32 mg protein and the gradient with the extract from the mutant membranes with 37 mg protein. The activities shown were calculated to the same amount of 37 mg protein to allow a direct comparison. Fractions of the gradients (numbered 1–20 from top to bottom) were collected and analyzed for NADH/ferricyanide oxidoreductase activity.