Background:The enzyme myeloperoxidase produces chlorine bleach at sites of inflammation. Results: 2-Thioxanthines are potent mechanism-based inactivators of myeloperoxidase. Conclusion: 2-Thioxanthines block production of chlorine bleach during inflammation. Significance: Mechanism-based inactivators of myeloperoxidase should limit oxidative stress at sites of inflammation.

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Background: Myeloperoxidase causes oxidative damage in many inflammatory diseases. Results: New substituted aromatic hydroxamates are identified as potent, selective, and reversible inhibitors of MPO. Conclusion: Binding affinities of hydroxamates to the heme pocket determine the potency of inhibition. Significance: Compounds that bind tightly to the active site of myeloperoxidase have potential as therapeutically useful inhibitors of oxidative stress.

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p47(phox) is an essential component of the NADPH oxidase, and phosphorylation of p47(phox) is associated with activation of the enzyme. Here we have used p47(phox) affinity chromatography to extract a p47(phox) kinase from neutrophil cytosol. The kinase activity was purified by gel filtration and Mini Q chromatography and shown to be indistinguishable from the catalytic fragments of protein kinase C (PKC)-beta(I), -beta(II) and -delta. The C-terminus of p47(phox) represented the site of interaction with PKC. Co-immunoprecipitation experiments revealed that the interaction between PKC isotypes and p47(phox) takes place in intact cells. However PKC-beta and -delta showed different time courses of co-immunoprecipitation, suggesting that the interactions may serve different functions for the various PKC isotypes. Using cells lacking p47(phox), we investigated the functional relevance of the interaction between PKC and p47(phox). Subcellular fractionation revealed an abnormal recruitment of PKC-beta(I) and -beta(II), but not PKC-delta, to particulate fractions in p47(phox)-deficient cells. Phosphorylation of cytosolic proteins was generally increased in stimulated p47(phox)-deficient neutrophils as compared with normal neutrophils. Furthermore, the cytoskeletal protein coronin was not phosphorylated upon stimulation of p47(phox)-deficient neutrophils. These findings were confirmed in an in vitro-reconstituted system using rat brain cytosol in which addition of p47(phox) affected phosphorylation by PKC/PKM (PKM is the catalytic fragment of PKC). These results indicate that p47(phox) can act as a regulator of PKC in neutrophils.