Defensin interferes with the activation of neutrophil NADPH oxidase in a cell-free system.

HNP-1 [correction of NHP-1], a member of a family of microbicidal cationic, cystine-rich polypeptides abundant in the azurophilic granules of polymorphonuclear leukocytes (PMN) interfered with detergent-induced cell-free activation of superoxide-producing NADPH oxidase. IC50 of 3 microM has been evaluated for this dose dependent effect of defensin. Preactivated oxidase was not affected by HNP-1. The inhibitory effect could be relieved by raising the concentration of the cytosol or by the addition of a partially purified p47-phox. NADPH oxidase activated in the presence of HNP-1 exhibited an increased affinity for NADPH.