The reduced folate carrier in L1210 murine leukemia cells is a 58-kDa protein

The reduced folate carrier (RFC1) is a major transporter for both natural r educed folates and antifolate chemotherapeutics. Using polyclonal antibodie s targeted to epitopes at the loop between the sixth and seventh predicted transmembrane domains or the distal C-terminus, we were able to demonstrate by Western blot analysis that the molecular size of RFC1 expressed in muri ne leukemia L1210 cells is 58 kDa as predicted by the open reading frame of its cDNA. 46-and 38-kDa proteins detected only in plasma membrane preparat ions were proteolytic degradation products that appeared during membrane pr eparation or treatment with the conventional SDS-PAGE loading buffer. These data resolve discrepancies reported previously for the molecular size of R FC1. (C) 2000 Elsevier Science B.V. All rights reserved.