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Figure S1. Structural determination of the BLT2 ligand from the rat intestine. (A) 1.5 nmol LTB4, 12-HHT, 12-HETE, and 15-HETE were analyzed by RP-HPLC (methanol/H2O/AcOH = 75:25:0.01), and fractions were collected every 1 min. The maximum absorbances of LTB4, 12-HHT, and 12/15-HETE are 270, 232, and 236 nm, respectively. (B) Acetone-soluble lipids from the rat intestine were analyzed by RP-HPLC (methanol/H2O/AcOH = 75:25:0.01), and fractions were collected every 1 min. The agonistic activity of each fraction toward CHO-BLT1 and -BLT2 cells was analyzed by cytosensor assay. (C) Fractions 12–14 from the rat intestine were analyzed by mass spectrometry using the enhanced mass scan mode. (D) The 279.2 (m/z) peak of fraction 13 was further analyzed by mass spectrometry using the enhanced resolution mode. (E) Structures of LTB4 and 12-HETE, candidate-calculated numerical values, and the corresponding formulas are shown.