Solubilization and characterization of leukotriene B4 receptor-GTP binding protein complex from porcine spleen

A high amount of leukotriene B4 (LTB4) binding protein was observed in the porcine spleen. It was solubilized and partially purified from spleen membrane with 3-(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). Scatchard analysis indicated the presence of a single class of receptor with Kd and Bmax values of 0.26 nM and 120 fmol/mg protein, respectively. The receptor was specific for LTB4, and Ki values for 20-hydroxy- and 20-carboxy-LTB4, both inactive metabolites of LTB4, were 1.7 nM and over 1,000 nM, respectively. By the addition of 10 microM GTP gamma S, a low affinity binding site appeared with a Kd value of 390 nM. A pretreatment of the receptor-GTP binding protein complex with islet-activating protein (IAP) increased the inhibitory effect of GTP gamma S on LTB4 binding, indicating that the LTB4 receptor is coupled with an IAP-sensitive GTP-binding protein in the porcine spleen.