The importance of hydroperoxide activation for the detection and assay of mammalian 5-lipoxygenase.

Sulfhydryl reagents such as dithiothreitol stabilized human leukocyte 5-lipoxygenase (5-LO) during purification. During enzyme assay, however, these reagents led to irreproducible or unexpectedly low activity. This inconsistency in the assay was eliminated by inclusion of hydroperoxyeicosatetraenoic acids (1-5 microM) during the reaction which effected a 10-20-fold stimulation of 5-LO activity. Structural studies indicated that an intact hydroperoxy function, and a long-chain fatty acyl moiety were required for 5-LO stimulation. These data suggest that human leukocyte 5-LO is activated by hydroperoxy fatty acids, and that this results in a requirement for exogenous hydroperoxide in the presence of sulfhydryl reagents.