Activation of NADPH-dependent superoxide production in a cell-free system by sodium dodecyl sulfate

Abstract

Sodium dodecyl sulfate (SDS) elicits the production of superoxide (O2-) by a cell-free system represented by sonically disrupted guinea pig peritoneal macrophages. O2- generation requires NADPH and a heat-sensitive cellular component, is proportional to the amount of macrophage protein, and exhibits a pH optimum of 6.5-7. The kinetic parameters of the SDS-stimulated enzyme are: Km (+/- S.E.) = 0.0367 +/- 0.003 mM NADPH and Vmax (+/- S.E.) = 73.46 +/- 9.09 nmol O2-/mg of protein/min. O2- production is dependent on the cooperation between a particulate subcellular component sedimentable at 48,000 X g and a cytosolic factor present in the 48,000 X g supernatant. The activity of both components is destroyed by heating at 80 degrees C. Pretreatment of intact macrophages with phorbol myristate acetate results in the partial removal of the requirement for cytosolic factor; SDS is now capable of activating the isolated 48,000 X g pellet. Among a large number of anionic, cationic, and nonionic detergents tested, only the anionic detergents SDS and sodium dodecyl sulfonate are capable of eliciting O2- production in the cell-free system, SDS being the more potent stimulant. It is proposed that the structural requirements that make these compounds capable of activating the O2- forming NADPH oxidase in a cell-free system are the presence of an anionic polar head and a long hydrophobic alkyl tail. We suggest that sodium salts of long chain unsaturated fatty acids that were found by us to be capable of stimulating O2- production in a cell-free system (Bromberg, Y., and Pick, E. (1984) Cell. Immunol. 88, 213-221) owe their activity to the fact that they function as anionic detergents.