YCF1 is a yeast vacuole membrane transporter involved in resistance to Cd2+ and to exogenous glutathione S-conjugate precursors. MRP1 contributes to multidrug resistance (MDR) in tumor cells. MRP1 and YCF1 have extensive amino acid sequence homology (63% amino acid similarity). We expressed MRP1 or YCF1 in insect cell membranes and compared their functions to know more about their structure-function relationships. YCF1 and MRP1 with His epitopes were expressed in Sf21 insect cells; both of them in the plasma membrane. The ATP-dependent transport of [H-3]LTC4 in Sf/YCF1-His vesicles was osmotically sensitive and showed saturable kinetics with an apparent K-m of 758 nM for LTC4 and 94 mu M for ATP which were similar to those in yeast cells. The K-m of YCF1 for LTC, (758 nM) was sevenfold higher than that of MRP1 (108 nM), MK-571 and ONO-1078, reversing agents for MRP1-mediated MDR, considerably inhibited the transport of LTC4 by both YCF1 and MRP1, However, PAK-104P, a pyridine analog that reverses MDR associated with P-gp and MRP1, inhibited the transporting activity of MRP1 stronger than that of YCF1. KE1, another MDR reversing agent, moderately inhibited the transport of LTC, by MRP1 but not that of YCF1. In conclusion, we successfully expressed yeast YCF1 in Sf21 insect cells and found that the localization of the protein was different from that in yeast. The function of YCF1 in Sf21 insect cells was similar but not identical to that of MRP1.