In vitro uptake and metabolism of pteroylpolyglutamate by rat small intestine.

The digestion and cellular uptake of 14C-pteroylheptaglutamate (14C-PG-7) was studied using an isolated cell preparation from rat small intestine and by assay of folate conjugase (EC 3.4.23.10) in whole homogenates and brush border fractions of rat small intestinal mucosa. In the cell preparation, 14C-pteroylmonoglutamate (14C-PG-1), the principal degradation product of 14C-PG-7, was concentrated earlier in the cell fraction than in the extracellular fraction, while the concentrations equalized after 15 minutes. Incubation of cells with equimolar 14C-PG-7 and 3H-PG-1 was followed by a threefold greater cellular concentration of 14C-PG-1 than 3H-PG-1. In subcellular fractionation studies, folate conjugase was minimally present in the brush border relative to the supernatant fraction. These data suggest that 14C-PG-7 is transported into the epithelial cell of the intestinal mucosa prior to its hydrolysis by intracellular folate conjugase.