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In vitro Uptake and Metabolism of Pteroylpolyglutamate by Rat Small Intestine^1,2,3,

Department of Internal Medicine, University of California, Davis, California 95616, and Department of Physiological Biochemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

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 3.4.12.10) 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.

KEY WORDS: • pteroylheptaglutamate • intestinal mucosal cell metabolism • folate conjugase

¹ Address reprint requests to Charles H. Halsted, M.D., Department of Internal Medicine, University of California, Davis, California 95616.

² This work was supported by Clinical Investigator Award 1 K08AM 70293 and Grants 1 R01 AM 18330 and 5 R01 AM 08644 from the National Institutes of Health. Bethesda, Maryland, Award No. 465 from the Nutrition Foundation. New York, Grant 1C-3M from the American Cancer Society and Grant BM 574-17348 from The National Science Foundation.

³ A preliminary report of this work was presented at the American Federation for Clinical Research, Atlantic City, N.J., May 5, 1974 and published in abstract form. Clin. Res. 22, 359.

Manuscript received 26 September 1975.