Membrane and tissue distribution of folate binding protein in pig.

Folate binding protein may participate in folate homeostasis by regulating monoglutamyl folate transport across relevant cell membranes. We compared the activity, immunoreactivity, and transcripts of folate binding protein in pig liver, kidney, and jejunal mucosa and their relevant cell membranes. Binding of [3H]folic acid was sixfold greater to pig liver plasma membranes than to kidney brush-border membranes, whereas there was no binding to jejunal brush-border membranes. The IgG fraction of rabbit antibody detected pig recombinant folate binding protein at 30 kDa and stained pig liver plasma membranes and kidney brush-border membranes but did not react with jejunal brush-border membranes. Folate binding protein transcripts were present in threefold greater abundance in pig liver than in kidney. Species comparisons showed folate binding protein transcripts in rat and human kidney but not in liver. Thus folate binding protein participates in folate homeostasis by regulating uptake by renal tubular membranes and uniquely by pig liver plasma membranes, but it is not involved in jejunal folate absorption.