Effects of metabolic inhibitors and lectins on the menadione-dependent generation of H2O2 by rat thymocytes.

The capacity of oxidative metabolism and its regulation is an important factor in disease control. Using scopoletin as a fluorescent substrate of peroxidase the extent of menadione-dependent production of H2O2 by rat thymocytes was determined. The reaction was inhibited by 2,4-dinitrophenol, papaverine, nordihydroguaiaretic acid and iodacetamide. The membrane-penetrating SH reagent N-ethylmaleimide primed the reaction, probably due to an inhibition of glutathione peroxidase. To delineate an influence of cell-surface protein-carbohydrate interactions by exogenous lectins, the impact of cell binding was analyzed for several plant lectins, namely concanavalin A, phytohemagglutinin, the lectins from Triticum vulgaris and from Sambucus nigra. Except for the alpha-NeuNAc(2-6)gal/galNAc-binding agglutinin, the other three plant proteins with specificities to different parts of N-linked oligosaccharides primed the reaction. This activity of lectins did not coincide with their ability to aggregate cells. The given results indicate that biosignaling pathways triggered by lectins are involved in the regulation of the intracellular reduction of menadione.