The subcellar particulate NADPH-dependent O_2.^-generating oxidase from human blood monocytes: Comparison to the neutrophil system

Highly purified preparations of normal human monocytes obtained from peripheral blood were shown to contain a subcellular particulate O_2.^-generating oxidase system. This O_2.^-generating activity was present in particulate preparations from monocytes that had been previously stimulated with phorbol myristate acetate but was low or absent in control preparations from unstimulated monocytes or stimulated monocytes from a patient with chronic granulomatous disease. In the stimulated preparations from normal monocytes O_2.^-generation was linearly proportional to cell protein concentration, insensitive to inhibition by azide, and dependent on NADPH as substrate. These characteristics are similar to the O_2.^-generating oxidase system from human neutrophils. A significant difference in the apparent K(m) for NADPH was shown between preparations from stimulated monocytes and neutrophils (monocyte 83 ± 16 µM, neutrophil 31 ± 5 µM, mean ± SE). Additionally, affinity of the stimulated monocyte particulate preparation for NADH was unmeasurably low.