Uptake of [3H]pteroylglutamic acid [(3H]PteGlu) was studied in microvilli isolated from the syncytiotrophoblast of the human term placenta. The effect of changes in medium osmolality on the equilibrium uptake of [3H]PteGlu was negligible, which suggested that the observed uptake represented binding to proteins on or within the microvilli rather than translocation of the vitamin from the incubation medium to a free state in the intravesicular fluid. Equilibrium uptake experiments performed over a wide range of [3H]PteGlu concentrations disclosed a class of binding sites with an association constant of 0.3 nM-1 as well as a second class of sites with high capacity and low affinity. Binding of [3H]PteGlu at the high-affinity sites was inhibited by tetrahydrofolate and N5-methyltetrahydrofolate, but not by several other structural analogues. It is likely that the high-affinity binding sites are receptors for maternal plasma folate; however, their role in placental transport or storage of the vitamin was not delineated in these studies.
Research Article|February 15 1984
Human placental microvilli contain high-affinity binding sites for folate
Biochem J (1984) 218 (1): 75-80.
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T Green, H C Ford; Human placental microvilli contain high-affinity binding sites for folate. Biochem J 15 February 1984; 218 (1): 75–80. doi: https://doi.org/10.1042/bj2180075
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