Binding of leukotriene C4 by glutathione transferase: a reassessment of biochemical and functional criteria for leukotriene receptors.

Studies of the molecular structures and biological activities of leukotrienes (LTs) provided evidence for the presence of multiple, subclass-specific receptors on the surface of responding tissues. Distinct receptors for LTC4 and LTD4 have been defined based on functional and metabolic criteria. However, radioligand-binding studies of LTC4-binding sites revealed anomalous results that failed to demonstrate a parallel relationship between binding affinity and functional activity for a number of agonists. In this study, we identified a high-affinity binding unit for LTC4 as the Ya subunit containing glutathione transferases (EC 2.5.1.18) that is present in both the cytosolic and the membrane fractions of rat liver homogenate. This enzyme accounted for a substantial portion of the LTC4-binding activity in rat liver cytosol as well as in mitochondrial and microsomal fractions. We suggest that the LTC4-binding sites in tissues are heterogeneous and that some binding units may have functions other than transduction of a signal across the cell membrane.