Abstract
THE small intestine of mammals possesses at least three independent active transport processes for the absorption of organic compounds: one for monosaccharides like glucose and galactose1; one for L-amino-acids2; and one for pyrimidines like uracil and thymine3. These specialized absorption processes have a number of characteristics in common which distinguish them from the process of simple diffusion: the substrate is transferred against a concentration gradient; the transport systems become saturated at high concentrations of substrate; and one substrate depresses the passage of another by competing with it for the transport process.
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SCHANKER, L., JEFFREY, J. Active Transport of Foreign Pyrimidines across the Intestinal Epithelium. Nature 190, 727–728 (1961). https://doi.org/10.1038/190727a0
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DOI: https://doi.org/10.1038/190727a0
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