Use of an affinity label to probe the function of the NADPH binding component of the respiratory burst oxidase of human neutrophils

Abstract

The respiratory burst oxidase of neutrophils can be activated in a cell-free system in which solubilized membranes, cytosol, and Mg2+ are required and in which sodium dodecyl sulfate is used to convert the dormant oxidase to an active form. The 2',3'-dialdehyde analog of NADPH was used as an affinity label for the cytosolic NADPH binding component of the respiratory burst oxidase from human neutrophils. When treated with this affinity label in the presence of sodium cyanoborohydride to reduce Schiff bases, neutrophil cytosol was shown to lose at least 90% of its activity in the cell-free system. In contrast to normal cytosol, treated cytosol had lost its ability to abolish the lag time required for activation of the oxidase, suggesting that the treated cytosol was no longer able to participate in the rate-limiting activation step. Furthermore, the treated cytosol had lost its ability to convert the oxidase from a form with a high Km to a form with a low Km for NADPH. The ability of dialdehyde-treated cytosol to activate the oxidase could be restored by untreated cytosol with a concentration dependence suggesting that only one kinetically active component of the oxidase was inhibited by treatment with the NADPH analog. Like the dialdehyde-treated cytosol, cytosols from patients with chronic granulomatous disease caused by a deficiency in a cytosolic Mr = 47,000 protein (pp47) fail to participate in the rate-limiting activation step (Curnutte, J. T., Scott, P. J., and Babior, B. M. (1989) J. Clin. Invest. 83, 1236-1240). These chronic granulomatous disease cytosols were nevertheless able to restore limited activity to the dialdehyde-inactivated cytosol in a cell-free activation system. These results are consistent with a model in which (a) the NADPH binding subunit of the oxidase exists in a very slowly dissociating complex with one or more additional cytosolic components, including pp47, and (b) the NADPH binding component of the oxidase controls the affinity of the enzyme for NADPH, either directly or through the binding of additional cytosolic factors.